I've previously posted here: http://forum.bitcoin.org/index.php?topic=22683.0
but that thread is now much too narrow in scope, so I decided to start a new one.
On Ubuntu, I'm running DiaboMiner and mining for slush. It's working great, with less than 1% of my blocks being rejected, except for a mysterious problem where the hash rate drops from 70 to 50 Mhash/s after I close the laptop's lid for a while. However, on Windows, I can't mine without an extremely high error rate. With DiabloMiner, roughly 40% of my blocks are rejected. On Phoenix, it's approximately 10%. I've tried ATI Stream v.2.1, v.2.4, Catalyst 10.11, and Catalyst 11.06. There seems to be no difference in terms of error rate.
Has anybody else encountered the same problem? I'm really hoping that someone has a solution!