I can confirm this, and my password also includes a % sign. But the weird thing is that when you start the program with gksu the unlock button is grey, but you still haven't got the rights you should have as root user. This applies not only to users-admin, but also to other programs included with gnome-system-tools. I can't even change my own password, since that also requires your password.
** Changed in: gnome-system-tools (Ubuntu) Status: New => Confirmed -- Cannot authenticate user https://bugs.launchpad.net/bugs/200634 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs