Nitin,
This is indicitive of a bad installation or an incompatible version of Eclipse being used. The easiest way to correct the issue is to install a new instance of Eclipse 3.1 (final) and then install MyEclipse 4.0GA such that it points to this new installation. Once you’ve done that, you can then open your existing workspace to return to development.
If you have any more problems after doing the above, can you please post all the information we request in the [URL=http://www.myeclipseide.com/PNphpBB2+file-viewtopic-t-393.html]Posting Guidelines[/URL] thread at the top of this forum? That will give us some context so that we can determine what’s going on.