I used to have these problems... but I fixed it by deleting the old drivers completely and downloading the new ones. I think it's because the video card is still somewhat "hung up" on the old driver? I don't know haha
Just Got a X1950Pro, upgraded from a X850XT which had No Problems with regards to AA/AF running the omega drivers.
BUT Now,
No AA/AF from Omega, Cat 7.9, Warcat, Cat 7.4...
Found the solution running Max Quality Profile with the ATT... Had no idea this issue existed... sucked trying all these drivers not knowing what was causing it.