Eclipse won't start, log error says: ObjectNotFoundException: Tree element

Question

Last night my machine restarted while Eclipse Galileo was open. No big deal, right?

This morning, I started my machine and tried to open Eclipse. Instead of opening, I see this:

The error log suggests that there is some kind of problem caused by exiting with unsaved changes.

How can I get Eclipse to open and ignore those unsaved changes? I can't even open a text file that is not part of this project with Eclipse? There must be a way to reset this state.

EDIT:

I have tracked down the problem to a single file. When I delete this file below, Eclipse opens but my projects are missing.

.metadata\.plugins\org.eclipse.core.resources\.snap

I do use the subversion plugin, but I don't think that is the problem. Here is what the error log says ( abbreviated ):

!SESSION 2010-08-17 10:13:01.718 -----------------------------------------------
eclipse.buildId=M20100211-1343
java.version=1.4.2_06
java.vendor=Sun Microsystems Inc.
BootLoader constants: OS=win32, ARCH=x86, WS=win32, NL=en_CA
Command-line arguments:  -os win32 -ws win32 -arch x86

!ENTRY org.eclipse.core.resources 2 10035 2010-08-17 10:13:02.656
!MESSAGE The workspace exited with unsaved changes in the previous session; refreshing workspace to recover changes.

!ENTRY org.eclipse.osgi 4 0 2010-08-17 10:13:02.671
!MESSAGE An error occurred while automatically activating bundle org.eclipse.core.resources (33).
!STACK 0
org.osgi.framework.BundleException: Exception in org.eclipse.core.resources.ResourcesPlugin.start() of bundle org.eclipse.core.resources.
    at org.eclipse.osgi.framework.internal.core.BundleContextImpl.startActivator(BundleContextImpl.java:806)
    at org.eclipse.osgi.framework.internal.core.BundleContextImpl.start(BundleContextImpl.java:755)
...

Caused by: org.eclipse.core.internal.dtree.ObjectNotFoundException: Tree element '/reports/src/com/lang/reports/OnlineReport.java' not found.
    at org.eclipse.core.internal.dtree.AbstractDataTree.handleNotFound(AbstractDataTree.java:257)
...

Root exception:
org.eclipse.core.internal.dtree.ObjectNotFoundException: Tree element '/reports/src/com/lang/reports/OnlineReport.java' not found.
    at org.eclipse.core.internal.dtree.AbstractDataTree.handleNotFound(AbstractDataTree.java:257)
...

!ENTRY org.eclipse.osgi 4 0 2010-08-17 10:13:02.703
!MESSAGE Application error
!STACK 1
java.lang.NoClassDefFoundError: org/eclipse/core/resources/IContainer
    at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:114)
    at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:194)

!ENTRY org.eclipse.osgi 2 0 2010-08-17 10:13:02.765
!MESSAGE The following is a complete list of bundles which are not resolved, see the prior log entry for the root cause if it exists:
!SUBENTRY 1 org.eclipse.osgi 2 0 2010-08-17 10:13:02.765
!MESSAGE Bundle org.eclipse.jdt.apt.core_3.3.202.R35x_v20091130-2300 [103] was not resolved.
!SUBENTRY 1 org.eclipse.osgi 2 0 2010-08-17 10:13:02.765
!MESSAGE Bundle org.eclipse.jdt.apt.pluggable.core_1.0.201.R35x_v20090925-1100 [104] was not resolved.
!SUBENTRY 2 org.eclipse.jdt.apt.pluggable.core 2 0 2010-08-17 10:13:02.765
!MESSAGE Missing required bundle org.eclipse.jdt.apt.core_0.0.0.
!SUBENTRY 2 org.eclipse.jdt.apt.pluggable.core 2 0 2010-08-17 10:13:02.765
!MESSAGE Missing imported package org.eclipse.jdt.internal.compiler.tool_0.0.0.
!SUBENTRY 2 org.eclipse.jdt.apt.pluggable.core 2 0 2010-08-17 10:13:02.765
!MESSAGE Missing imported package org.eclipse.jdt.internal.compiler.apt.dispatch_0.0.0.
!SUBENTRY 2 org.eclipse.jdt.apt.pluggable.core 2 0 2010-08-17 10:13:02.765
!MESSAGE Missing imported package org.eclipse.jdt.internal.compiler.apt.model_0.0.0.
!SUBENTRY 2 org.eclipse.jdt.apt.pluggable.core 2 0 2010-08-17 10:13:02.765
!MESSAGE Missing imported package org.eclipse.jdt.internal.compiler.apt.util_0.0.0.
!SUBENTRY 1 org.eclipse.osgi 2 0 2010-08-17 10:13:02.765
!MESSAGE Bundle org.eclipse.jdt.apt.ui_3.3.200.v20090930-2100_R35x [105] was not resolved.
!SUBENTRY 2 org.eclipse.jdt.apt.ui 2 0 2010-08-17 10:13:02.765
!MESSAGE Missing required bundle org.eclipse.jdt.apt.core_[3.2.0,4.0.0).
!SUBENTRY 1 org.eclipse.osgi 2 0 2010-08-17 10:13:02.765
!MESSAGE Bundle org.eclipse.jdt.compiler.apt_1.0.201.R35x_v20090925-1100 [106] was not resolved.
!SUBENTRY 2 org.eclipse.jdt.compiler.apt 2 0 2010-08-17 10:13:02.765
!MESSAGE Missing imported package org.eclipse.jdt.internal.compiler.tool_0.0.0.
!SUBENTRY 1 org.eclipse.osgi 2 0 2010-08-17 10:13:02.765
!MESSAGE Bundle org.eclipse.jdt.compiler.tool_1.0.100.v_981_R35x [107] was not resolved.
!SUBENTRY 1 org.eclipse.osgi 2 0 2010-08-17 10:13:02.765
!MESSAGE Bundle org.eclipse.jdt.junit4.runtime_1.1.0.v20090513-2000 [116] was not resolved.
!SUBENTRY 2 org.eclipse.jdt.junit4.runtime 2 0 2010-08-17 10:13:02.765
!MESSAGE Missing required bundle org.junit4_[4.4.0,5.0.0).
!SUBENTRY 1 org.eclipse.osgi 2 0 2010-08-17 10:13:02.765
!MESSAGE Bundle org.hamcrest.core_1.1.0.v20090501071000 [184] was not resolved.
!SUBENTRY 1 org.eclipse.osgi 2 0 2010-08-17 10:13:02.765
!MESSAGE Bundle org.junit4_4.5.0.v20090824 [186] was not resolved.
!SUBENTRY 2 org.junit4 2 0 2010-08-17 10:13:02.765
!MESSAGE Missing required bundle org.hamcrest.core_1.1.0.
!SUBENTRY 1 org.eclipse.osgi 2 0 2010-08-17 10:13:02.765
!MESSAGE Bundle com.collabnet.subversion.merge_2.1.0 [208] was not resolved.

Answer 1

For this issue I had to delete the .snap file located in the directory :

<workspace-directory>\.metadata\.plugins\org.eclipse.core.resources

After deleting that file, I was able to start my Eclipse with no problem.

Answer 2

Recommended: Delete <workspace-directory>\.metadata\.plugins\org.eclipse.core.resources\.snap. This will not reset your workspace and your other projects won't get deleted (as answered by krishna).

Not Recommended: Alternatively, delete the the whole <workspace-directory>\.metadata directory from your workspace and restart.This will reset your workspace and delete all your existing projects in it.

Answer 3

Ran into this error.

There was no .snap file in my .metadata folder.

I had to delete this:

<workspace>/.metadata/.plugins/org.eclipse.core.resources/.root/d+.tree

d+=> some number.

Then I had to re-import the projects and re-assign the working sets. I preferred it over opening a new workspace and redoing settings.

Answer 4

Deleting .snap file worked perfect for me.

1. Delete .snap file from the directory - workspace.metadata.plugins\org.eclipse.core.resources.
2. Import the workspace (existing projects into workspace - do not copy folders into workspace again).