[ubuntu] Graphic card and unity desktop???

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http://ubuntuforums.org – I just don't know how to name this thread to describe this problem. I have a laptop dell vostro 3550 (2 graphic card: Intel HD 3000 and ATI HD 6630) on which I installed ubuntu 11.04 (32bits) and i can use unity desktop environment on the first boot. When the Additional Drivers told me to activate ATI drivers, I click on activate and after that restarted the laptop. When ubuntu boot up, it said that:"you do not have the hardware required to run Unity" I opened System->Preferences->ATI Catalyst Control Center An error occured: Code: There was a problem initializing Catalys (Hardware)