Comment 15 for bug 431147

It only affects gdmsetup from my experience. Although I am not sure what causes it, something blocks it from opening the org.freedesktop.systemtoolsbackends.set authentication window.

To everyone out there who is not able to unlock users-admin (Tyson, Guido, Pedro, Neal) please try to answer the following:
-Are/Were you on an upgraded system (9.04 -> 9.10) or a clean install on Ubuntu 9.10?
-Have/Had you fully updated your system using Update Manager (If so, you should be running linux 2.6.31-16, run 'uname -r' to check)