This is always caused by an installation issue, either using incompatible versions of Eclipse and/or MyEclipse or not using the Eclipse SDK.
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 if this is an installation issue, a configuration problem, or a bug. Thanks.