The culprit is the xgl/compiz repository. It is unofficial and causes some problems like this. Try to remove and reinstall the problematic packages. Also I think this bug can be rejected as these are unofficial repositories, can someone confirm?
-- Can't install 'ubuntu-desktop' https://launchpad.net/bugs/63205 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
