"Gradle files have changed since last project sync." message always shows up

Question

I'm working on an Android Studio project of which I write while constantly move back and forth from laptop to desktop using usb stick. There has been no problem for couple of months I tried this since Android Studio went stable, until today this message keeps showing up no matter how many times I sync the gradle:

Gradle files have changed since last project sync. A project sync may be necessary for the IDE to work properly.

Gradle Console indicates that the build is successful. I also tried cleaning and rebuilding the project, even reinstalling Android Studio, still the message pops out.

What seems to be the problem? Is it not recommended to write a project on multiple Android Studios?

Here's a look of my build.gradle:

apply plugin: 'com.android.application'

android {
compileSdkVersion 21
buildToolsVersion "21.1.2"

defaultConfig {
    applicationId "com.simplifyinc.prodigy"
    minSdkVersion 16
    targetSdkVersion 21
    versionCode 1
    versionName "0.3.2"
}
buildTypes {
    release {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }
}

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile 'com.android.support:appcompat-v7:21.0.3'
    compile 'de.hdodenhof:circleimageview:1.2.1'
    compile 'com.oguzdev:CircularFloatingActionMenu:1.0.2'
    compile 'net.the4thdimension:audio-wife:1.0.3'
    compile project('libraries:android-crop')
}

Answer 1

in build.gradle(module:app) change build tool,( in my case its 23.0.1) targetSdkVersion (23) and in dependency compile version
("com.android.support:appcompat-v7:23.1.0") to latest This happens due to gradle updates

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