from my experience, I got to say it is a driver issue. You need to go to the MFG and look at the drivers for the video card. ATI had about written Windows 7 64bit drivers for their VC. "about" being the word. 5770 doesn't and seems want. I don't think CL will write one or they would and stop the negative and time consumming dialogue.
If there isn't a Windows 7 64bit driver, then bite the bullet and get a new VC, make sure it has one. PNY web site shows news VC coming out. Specs are great if laget. Prices are definitly reduced. I would have to wait but would have saved myself $70, what's money compared to frustration and stress?
Amature does it till he gets it right. A Pro does it till he can't get it wrong.