Maven java.lang.ClassNotFoundException: org.codehaus.plexus.classworlds.launcher.Launcher

Have you ever faced exception like this?

Exception in thread "main" java.lang.NoClassDefFoundError: org/codehaus/plexus/classworlds/launcher/Launcher
Caused by: java.lang.ClassNotFoundException: org.codehaus.plexus.classworlds.launcher.Launcher
        at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
Could not find the main class: org.codehaus.plexus.classworlds.launcher.Launcher.  Program will exit.

My use case was that I had installed maven3 and afterwards tried to use maven2. All the environment variables updates have been setup in:

~/.bashrc

However once trying to use maven2 exception appeared (Even in the new terminal session).
Solution was found based on advice present in: http://cyntech.wordpress.com/2011/03/09/maven-2-error/

Running command:

which mvn

revealed the problem, as I still had in my $PATH the maven3 binary. Even if I appended the maven2, it was there on the later position => maven3 was to be used, but with changed $M2_HOME (reffering to maven 2).

Fixing the $PATH did the job for me.

This might not be your case, therefor as a general sum up of possible root causes, I recommend checking: http://stackoverflow.com/questions/6198677/java-lang-noclassdeffounderror-org-codehaus-plexus-classworlds-launcher-launche