I had this issue with GRID/PURE/DiRT games.
The fix for this is to load the latest AMD Multicore Driver. This was for my HTPC PC, which at the time had a x2 4400.
i7 930 @ 4.2Ghz
GIGABYTE x58 UD7
Kingston HyperX T1 Series 12GB
GIGABYTE 7970 (1280/1800)
OCZ Vertex 2 100GB SSD & VelociRaptor 300GB