I am working on PhoneGap BlackberryWebWorks i have install BlackBerry WebWorks plug-in:2.5.1 and Blackberry WebWorks SDK:2.0.0. and PhoneGap 0.9.4.but while building the project
As a more generic answer, this is because you either imported a project which is dependent on uninstalled Eclipse plugins. I had this issue when migrating to Eclipse Juno. The easiest solution, just edit your .project file in a text editor and remove the conflicting elements. Usually, this is in the buildspec or nature section.
org.eclipse.jdt.core.javabuilder
org.eclipse.m2e.core.maven2Builder
org.eclipse.m2e.core.maven2Nature
org.eclipse.jdt.core.javanature
Keep a backup of your project file if you're not sure. You may always delete and recreate your project later on. It's easier to remove those references than to find and install the exact missing plugin versions.