Is this the new Sapphire HD6950 oc ver were talking about here. I had multi problems when going from 12.3 to 12.4 along with this issue. I didn't install the 12.2 driver that came on the disk, I went with 12.3 and this is where I'm still at. Have you tried to drop the power tune bar down to under 0, save it, then slide it back up to 0, save it again. I read on one of the gaming forums that this worked for a few folks.
Gigabyte GA-MA790GPT-UD3H,Phenom II 955 BE C3 AM3 3.8
ZalmanLED9900A Cooler,Corsair xm3 DDR3 1600 8GB's ram
BFG 650 watts PW,,Antec 900II case
GGC-H20L BR multi drive,Sapphire 2GB HD6950oc
Windows 7 Ultimate x64