Maven error - java.lang.NoClassDefFoundError: org/slf4j/helpers/MarkerIgnoringBase

Question

Getting up and running with Maven.

Trying to build a project I've inherited. I've resolved majority of the issues but am now seeing a weird error:

[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 2.842 s
[INFO] Finished at: 2015-04-24T13:59:32+01:00
[INFO] Final Memory: 13M/308M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal com.day.jcr.vault:content-package-maven-plugin:0.0.20:package (default-package) on project website-view: Execution default-package of goal com.day.jcr.vault:content-package-maven-plugin:0.0.20:package failed: A required class was missing while executing com.day.jcr.vault:content-package-maven-plugin:0.0.20:package: org/slf4j/helpers/MarkerIgnoringBase
[ERROR] -----------------------------------------------------
[ERROR] realm =    extension>com.day.jcr.vault:content-package-maven-plugin:0.0.20
[ERROR] strategy = org.codehaus.plexus.classworlds.strategy.SelfFirstStrategy
[ERROR] urls[0] = file:/C:/Users/tim.clifford/.m2/repository/com/day/jcr/vault/content-package-maven-plugin/0.0.20/content-package-maven-plugin-0.0.20.jar
[ERROR] urls[1] = file:/C:/Users/tim.clifford/.m2/repository/backport-util-concurrent/backport-util-concurrent/3.1/backport-util-concurrent-3.1.jar
[ERROR] urls[2] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/plexus/plexus-interpolation/1.11/plexus-interpolation-1.11.jar
[ERROR] urls[3] = file:/C:/Users/tim.clifford/.m2/repository/junit/junit/3.8.1/junit-3.8.1.jar
[ERROR] urls[4] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/maven/maven-archiver/2.3/maven-archiver-2.3.jar
[ERROR] urls[5] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/plexus/plexus-archiver/1.0-alpha-9/plexus-archiver-1.0-alpha-9.jar
[ERROR] urls[6] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/plexus/plexus-io/1.0-alpha-1/plexus-io-1.0-alpha-1.jar
[ERROR] urls[7] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/plexus/plexus-utils/1.4.9/plexus-utils-1.4.9.jar
[ERROR] urls[8] = file:/C:/Users/tim.clifford/.m2/repository/org/sonatype/plexus/plexus-sec-dispatcher/1.3/plexus-sec-dispatcher-1.3.jar
[ERROR] urls[9] = file:/C:/Users/tim.clifford/.m2/repository/org/sonatype/plexus/plexus-cipher/1.4/plexus-cipher-1.4.jar
[ERROR] urls[10] = file:/C:/Users/tim.clifford/.m2/repository/commons-httpclient/commons-httpclient/3.1/commons-httpclient-3.1.jar
[ERROR] urls[11] = file:/C:/Users/tim.clifford/.m2/repository/commons-logging/commons-logging/1.0.4/commons-logging-1.0.4.jar
[ERROR] urls[12] = file:/C:/Users/tim.clifford/.m2/repository/commons-codec/commons-codec/1.2/commons-codec-1.2.jar
[ERROR] urls[13] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/mojo/animal-sniffer-maven-plugin/1.8/animal-sniffer-maven-plugin-1.8.jar
[ERROR] urls[14] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/mojo/animal-sniffer/1.8/animal-sniffer-1.8.jar
[ERROR] urls[15] = file:/C:/Users/tim.clifford/.m2/repository/org/ow2/asm/asm-all/4.0/asm-all-4.0.jar
[ERROR] urls[16] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/mojo/java-boot-classpath-detector/1.8/java-boot-classpath-detector-1.8.jar
[ERROR] urls[17] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/maven/reporting/maven-reporting-api/2.0.1/maven-reporting-api-2.0.1.jar
[ERROR] urls[18] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/maven/doxia/doxia-sink-api/1.0-alpha-6/doxia-sink-api-1.0-alpha-6.jar
[ERROR] urls[19] = file:/C:/Users/tim.clifford/.m2/repository/commons-cli/commons-cli/1.0/commons-cli-1.0.jar
[ERROR] urls[20] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/plexus/plexus-interactivity-api/1.0-alpha-4/plexus-interactivity-api-1.0-alpha-4.jar
[ERROR] urls[21] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/maven/shared/maven-common-artifact-filters/1.2/maven-common-artifact-filters-1.2.jar
[ERROR] urls[22] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/maven/shared/maven-plugin-testing-harness/1.1/maven-plugin-testing-harness-1.1.jar
[ERROR] urls[23] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/sling/org.apache.sling.commons.json/2.0.6/org.apache.sling.commons.json-2.0.6.jar
[ERROR] Number of foreign imports: 1
[ERROR] import: Entry[import  from realm ClassRealm[maven.api, parent: null]]
[ERROR] 
[ERROR] -----------------------------------------------------: org.slf4j.helpers.MarkerIgnoringBase
[ERROR] -> [Help 1]
org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal com.day.jcr.vault:content-package-maven-plugin:0.0.20:package (default-package) on project website-view: Execution default-package of goal com.day.jcr.vault:content-package-maven-plugin:0.0.20:package failed: A required class was missing while executing com.day.jcr.vault:content-package-maven-plugin:0.0.20:package: org/slf4j/helpers/MarkerIgnoringBase
-----------------------------------------------------
realm =    extension>com.day.jcr.vault:content-package-maven-plugin:0.0.20
strategy = org.codehaus.plexus.classworlds.strategy.SelfFirstStrategy
urls[0] = file:/C:/Users/tim.clifford/.m2/repository/com/day/jcr/vault/content-package-maven-plugin/0.0.20/content-package-maven-plugin-0.0.20.jar
urls[1] = file:/C:/Users/tim.clifford/.m2/repository/backport-util-concurrent/backport-util-concurrent/3.1/backport-util-concurrent-3.1.jar
urls[2] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/plexus/plexus-interpolation/1.11/plexus-interpolation-1.11.jar
urls[3] = file:/C:/Users/tim.clifford/.m2/repository/junit/junit/3.8.1/junit-3.8.1.jar
urls[4] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/maven/maven-archiver/2.3/maven-archiver-2.3.jar
urls[5] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/plexus/plexus-archiver/1.0-alpha-9/plexus-archiver-1.0-alpha-9.jar
urls[6] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/plexus/plexus-io/1.0-alpha-1/plexus-io-1.0-alpha-1.jar
urls[7] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/plexus/plexus-utils/1.4.9/plexus-utils-1.4.9.jar
urls[8] = file:/C:/Users/tim.clifford/.m2/repository/org/sonatype/plexus/plexus-sec-dispatcher/1.3/plexus-sec-dispatcher-1.3.jar
urls[9] = file:/C:/Users/tim.clifford/.m2/repository/org/sonatype/plexus/plexus-cipher/1.4/plexus-cipher-1.4.jar
urls[10] = file:/C:/Users/tim.clifford/.m2/repository/commons-httpclient/commons-httpclient/3.1/commons-httpclient-3.1.jar
urls[11] = file:/C:/Users/tim.clifford/.m2/repository/commons-logging/commons-logging/1.0.4/commons-logging-1.0.4.jar
urls[12] = file:/C:/Users/tim.clifford/.m2/repository/commons-codec/commons-codec/1.2/commons-codec-1.2.jar
urls[13] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/mojo/animal-sniffer-maven-plugin/1.8/animal-sniffer-maven-plugin-1.8.jar
urls[14] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/mojo/animal-sniffer/1.8/animal-sniffer-1.8.jar
urls[15] = file:/C:/Users/tim.clifford/.m2/repository/org/ow2/asm/asm-all/4.0/asm-all-4.0.jar
urls[16] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/mojo/java-boot-classpath-detector/1.8/java-boot-classpath-detector-1.8.jar
urls[17] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/maven/reporting/maven-reporting-api/2.0.1/maven-reporting-api-2.0.1.jar
urls[18] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/maven/doxia/doxia-sink-api/1.0-alpha-6/doxia-sink-api-1.0-alpha-6.jar
urls[19] = file:/C:/Users/tim.clifford/.m2/repository/commons-cli/commons-cli/1.0/commons-cli-1.0.jar
urls[20] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/plexus/plexus-interactivity-api/1.0-alpha-4/plexus-interactivity-api-1.0-alpha-4.jar
urls[21] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/maven/shared/maven-common-artifact-filters/1.2/maven-common-artifact-filters-1.2.jar
urls[22] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/maven/shared/maven-plugin-testing-harness/1.1/maven-plugin-testing-harness-1.1.jar
urls[23] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/sling/org.apache.sling.commons.json/2.0.6/org.apache.sling.commons.json-2.0.6.jar
Number of foreign imports: 1
import: Entry[import  from realm ClassRealm[maven.api, parent: null]]

-----------------------------------------------------

    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:224)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:116)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:80)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:51)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:128)
    at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:307)
    at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:193)
    at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:106)
    at org.apache.maven.cli.MavenCli.execute(MavenCli.java:862)
    at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:286)
    at org.apache.maven.cli.MavenCli.main(MavenCli.java:197)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)
Caused by: org.apache.maven.plugin.PluginExecutionException: Execution default-package of goal com.day.jcr.vault:content-package-maven-plugin:0.0.20:package failed: A required class was missing while executing com.day.jcr.vault:content-package-maven-plugin:0.0.20:package: org/slf4j/helpers/MarkerIgnoringBase
-----------------------------------------------------
realm =    extension>com.day.jcr.vault:content-package-maven-plugin:0.0.20
strategy = org.codehaus.plexus.classworlds.strategy.SelfFirstStrategy
urls[0] = file:/C:/Users/tim.clifford/.m2/repository/com/day/jcr/vault/content-package-maven-plugin/0.0.20/content-package-maven-plugin-0.0.20.jar
urls[1] = file:/C:/Users/tim.clifford/.m2/repository/backport-util-concurrent/backport-util-concurrent/3.1/backport-util-concurrent-3.1.jar
urls[2] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/plexus/plexus-interpolation/1.11/plexus-interpolation-1.11.jar
urls[3] = file:/C:/Users/tim.clifford/.m2/repository/junit/junit/3.8.1/junit-3.8.1.jar
urls[4] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/maven/maven-archiver/2.3/maven-archiver-2.3.jar
urls[5] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/plexus/plexus-archiver/1.0-alpha-9/plexus-archiver-1.0-alpha-9.jar
urls[6] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/plexus/plexus-io/1.0-alpha-1/plexus-io-1.0-alpha-1.jar
urls[7] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/plexus/plexus-utils/1.4.9/plexus-utils-1.4.9.jar
urls[8] = file:/C:/Users/tim.clifford/.m2/repository/org/sonatype/plexus/plexus-sec-dispatcher/1.3/plexus-sec-dispatcher-1.3.jar
urls[9] = file:/C:/Users/tim.clifford/.m2/repository/org/sonatype/plexus/plexus-cipher/1.4/plexus-cipher-1.4.jar
urls[10] = file:/C:/Users/tim.clifford/.m2/repository/commons-httpclient/commons-httpclient/3.1/commons-httpclient-3.1.jar
urls[11] = file:/C:/Users/tim.clifford/.m2/repository/commons-logging/commons-logging/1.0.4/commons-logging-1.0.4.jar
urls[12] = file:/C:/Users/tim.clifford/.m2/repository/commons-codec/commons-codec/1.2/commons-codec-1.2.jar
urls[13] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/mojo/animal-sniffer-maven-plugin/1.8/animal-sniffer-maven-plugin-1.8.jar
urls[14] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/mojo/animal-sniffer/1.8/animal-sniffer-1.8.jar
urls[15] = file:/C:/Users/tim.clifford/.m2/repository/org/ow2/asm/asm-all/4.0/asm-all-4.0.jar
urls[16] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/mojo/java-boot-classpath-detector/1.8/java-boot-classpath-detector-1.8.jar
urls[17] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/maven/reporting/maven-reporting-api/2.0.1/maven-reporting-api-2.0.1.jar
urls[18] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/maven/doxia/doxia-sink-api/1.0-alpha-6/doxia-sink-api-1.0-alpha-6.jar
urls[19] = file:/C:/Users/tim.clifford/.m2/repository/commons-cli/commons-cli/1.0/commons-cli-1.0.jar
urls[20] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/plexus/plexus-interactivity-api/1.0-alpha-4/plexus-interactivity-api-1.0-alpha-4.jar
urls[21] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/maven/shared/maven-common-artifact-filters/1.2/maven-common-artifact-filters-1.2.jar
urls[22] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/maven/shared/maven-plugin-testing-harness/1.1/maven-plugin-testing-harness-1.1.jar
urls[23] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/sling/org.apache.sling.commons.json/2.0.6/org.apache.sling.commons.json-2.0.6.jar
Number of foreign imports: 1
import: Entry[import  from realm ClassRealm[maven.api, parent: null]]

-----------------------------------------------------

    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:168)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:208)
    ... 20 more
Caused by: org.apache.maven.plugin.PluginContainerException: A required class was missing while executing com.day.jcr.vault:content-package-maven-plugin:0.0.20:package: org/slf4j/helpers/MarkerIgnoringBase
-----------------------------------------------------
realm =    extension>com.day.jcr.vault:content-package-maven-plugin:0.0.20
strategy = org.codehaus.plexus.classworlds.strategy.SelfFirstStrategy
urls[0] = file:/C:/Users/tim.clifford/.m2/repository/com/day/jcr/vault/content-package-maven-plugin/0.0.20/content-package-maven-plugin-0.0.20.jar
urls[1] = file:/C:/Users/tim.clifford/.m2/repository/backport-util-concurrent/backport-util-concurrent/3.1/backport-util-concurrent-3.1.jar
urls[2] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/plexus/plexus-interpolation/1.11/plexus-interpolation-1.11.jar
urls[3] = file:/C:/Users/tim.clifford/.m2/repository/junit/junit/3.8.1/junit-3.8.1.jar
urls[4] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/maven/maven-archiver/2.3/maven-archiver-2.3.jar
urls[5] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/plexus/plexus-archiver/1.0-alpha-9/plexus-archiver-1.0-alpha-9.jar
urls[6] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/plexus/plexus-io/1.0-alpha-1/plexus-io-1.0-alpha-1.jar
urls[7] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/plexus/plexus-utils/1.4.9/plexus-utils-1.4.9.jar
urls[8] = file:/C:/Users/tim.clifford/.m2/repository/org/sonatype/plexus/plexus-sec-dispatcher/1.3/plexus-sec-dispatcher-1.3.jar
urls[9] = file:/C:/Users/tim.clifford/.m2/repository/org/sonatype/plexus/plexus-cipher/1.4/plexus-cipher-1.4.jar
urls[10] = file:/C:/Users/tim.clifford/.m2/repository/commons-httpclient/commons-httpclient/3.1/commons-httpclient-3.1.jar
urls[11] = file:/C:/Users/tim.clifford/.m2/repository/commons-logging/commons-logging/1.0.4/commons-logging-1.0.4.jar
urls[12] = file:/C:/Users/tim.clifford/.m2/repository/commons-codec/commons-codec/1.2/commons-codec-1.2.jar
urls[13] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/mojo/animal-sniffer-maven-plugin/1.8/animal-sniffer-maven-plugin-1.8.jar
urls[14] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/mojo/animal-sniffer/1.8/animal-sniffer-1.8.jar
urls[15] = file:/C:/Users/tim.clifford/.m2/repository/org/ow2/asm/asm-all/4.0/asm-all-4.0.jar
urls[16] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/mojo/java-boot-classpath-detector/1.8/java-boot-classpath-detector-1.8.jar
urls[17] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/maven/reporting/maven-reporting-api/2.0.1/maven-reporting-api-2.0.1.jar
urls[18] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/maven/doxia/doxia-sink-api/1.0-alpha-6/doxia-sink-api-1.0-alpha-6.jar
urls[19] = file:/C:/Users/tim.clifford/.m2/repository/commons-cli/commons-cli/1.0/commons-cli-1.0.jar
urls[20] = file:/C:/Users/tim.clifford/.m2/repository/org/codehaus/plexus/plexus-interactivity-api/1.0-alpha-4/plexus-interactivity-api-1.0-alpha-4.jar
urls[21] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/maven/shared/maven-common-artifact-filters/1.2/maven-common-artifact-filters-1.2.jar
urls[22] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/maven/shared/maven-plugin-testing-harness/1.1/maven-plugin-testing-harness-1.1.jar
urls[23] = file:/C:/Users/tim.clifford/.m2/repository/org/apache/sling/org.apache.sling.commons.json/2.0.6/org.apache.sling.commons.json-2.0.6.jar
Number of foreign imports: 1
import: Entry[import  from realm ClassRealm[maven.api, parent: null]]

-----------------------------------------------------

    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:166)
    ... 21 more
Caused by: java.lang.NoClassDefFoundError: org/slf4j/helpers/MarkerIgnoringBase
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:800)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
    at java.net.URLClassLoader.access$100(URLClassLoader.java:71)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:361)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
    at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClassFromSelf(ClassRealm.java:401)
    at org.codehaus.plexus.classworlds.strategy.SelfFirstStrategy.loadClass(SelfFirstStrategy.java:42)
    at org.codehaus.plexus.classworlds.realm.ClassRealm.unsynchronizedLoadClass(ClassRealm.java:271)
    at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClass(ClassRealm.java:247)
    at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClass(ClassRealm.java:239)
    at org.slf4j.impl.MavenLoggerFactory.<clinit>(MavenLoggerFactory.java:26)
    at org.slf4j.impl.StaticLoggerBinder.<init>(StaticLoggerBinder.java:41)
    at org.slf4j.impl.StaticLoggerBinder.<clinit>(StaticLoggerBinder.java:34)
    at com.day.jcr.vault.maven.pack.VaultMojo.execute(VaultMojo.java:237)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:134)
    ... 21 more
Caused by: java.lang.ClassNotFoundException: org.slf4j.helpers.MarkerIgnoringBase
    at org.codehaus.plexus.classworlds.strategy.SelfFirstStrategy.loadClass(SelfFirstStrategy.java:50)
    at org.codehaus.plexus.classworlds.realm.ClassRealm.unsynchronizedLoadClass(ClassRealm.java:271)
    at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClass(ClassRealm.java:247)
    at org.codehaus.plexus.classworlds.realm.ClassRealm.loadClass(ClassRealm.java:239)
    ... 40 more

Looks like somethign related to the content-package-maven-plugin plugin.

Would love any clues people can offer :)

Answer 1

This happened to me when doing:

brew upgrade

It automatically updated my maven version to 3.3.3 that seems to have some issues as I was getting exactly the same message as the original post.

My solution was:

brew uninstall maven                               // to get rid of 3.3.3
brew install homebrew/versions/maven32             // to install maven 
brew pin homebrew/versions/maven32                 // to prevent unintended upgrade

And then make sure you have a line like this on ~/.bash_profile pointing to the correct maven path:

export M2_HOME=~/usr/local/Cellar/maven32/3.2.5    ~/.bash_profile 

Answer 2

For all AEM users, who experience the same problem after generating a maven project with the archetype: I solved the problem by updating the version of the content-package-maven-plugin to version 0.0.24:

            <plugin>
                <groupId>com.day.jcr.vault</groupId>
                <artifactId>content-package-maven-plugin</artifactId>
                <version>0.0.24</version>
                <extensions>true</extensions>
                <configuration>
                    <failOnError>true</failOnError>
                    <username>${crx.username}</username>
                    <password>${crx.password}</password>
                </configuration>
            </plugin>