Is your password expired ? Can you try changing your password and see whether you are able to unlock with the new password ?
If you still see the problem can you post "/var/log/auth.log" after trying to unlock the screen. -- screen does not unlock after locking https://launchpad.net/bugs/76632 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
