I activated, or installed the Catalyst 11.8 driver, which is the non postrelease one, I think. When I go into Applications -> Other -> Catalyst Control Center, I get an error saying "There was a problem initializing Catalyst Control Center Linux edition..."
Also, when I open up a terminal and use
fglrxinfo I get a X error, it says BadRequest (invalid request code or no such operation).
I'm not using Unity, I'm using Gnome Classic.
Video card is a ATI Mobility Raedeon HD 5470.