I've been mining for a few days now and when I first started out, I couldn't submit any shares because it always returns a "Verification failed, check hardware!" warning.
I did some googling and it seems to be a common problem. I tried everything to no avail until I tried mining with Phoenix 1.7.5. Smooth as silk.
I'm not sure what's the difference between Phoenix and the other miners. Some enlightenment, anyone?
Phoenix is a good miner. Do you need a different one?
CGMiner's FAQ has driver and SDK suggestions. It is very difficult to back level the SDK if you installed 2.6 or later. So if you don't need SDK 2.6 for the 7xxx series cards be careful to never install it.
Sam