Sounds like a duplicate of Bug #14122. Could you please take a look there and see if that is your problem?
** Changed in: gksu (Ubuntu) Importance: Undecided => Medium Status: Unconfirmed => Needs Info -- gksu doesn't accept/rejects password, no choice but use sudo instead on feisty https://launchpad.net/bugs/90324 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs