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.
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.