Comment 8 for bug 187335

I had the same problem. I run 8.04 upgraded from 7.10 on a laptop with an attached screen. Two instances of gnome (no xinerama).

After checking that I had my account added to /etc/group to admin and polkitusers groups and reconfiguring the package i discovered that the button actually did work, however only on the laptop-screen.

If I start an administrative tool on my laptop screen everything works fine, but if i try to do the same on the external screen i get an "unexpected error".

This really seems like a bug in whatever voodoo that handles policykit. Like it can't bind to the correct window manager or something.