To debug authentication problems you want to use the test-passwd tool in the src directory or the gnome-screensaver sources.
This may be fixed by the patch in GNOME bug #387572. -- screen does not unlock after locking https://launchpad.net/bugs/76632 -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs
