Ok, I’ve now twice wasted time on trying to figure this out and this time I’m writing it down, so I don’t do it a third time 🙂
I recently added an eclipse project to SVN (it’s already in perforce, my usual SC of choice) and after that my JAR export would fail with a bunch of “Resource is out of sync” errors. Since all the resources were .svn related, I blamed SVN and chased this down the wrong path for a bit.
Here’s the simple solution: If you see a jar export fail because of “resource is out of sync”, try doing a Refresh on the project before anything else. That should solve it.