Missing required library in eclipse for non-required library

Re-adding the problematic jar, then removing it did the trick. This is better than reconfiguring the entire workspace in my case, as I have many projects, and ADT configuration in my workspace.

Please do the following, if one does not solve your problem, skip to the next one:

1. Check .classpath file in your project folder. You might have a reference there.
2. Close and re-open the project without closing eclipse, this might rebuild Eclipse resource cache.
3. Make a clean build after re-opening.
4. Re-import your project into a clean workspace.