Did you try 12.1 ( custom install with no sdk/app ) with the 2.1 sdk install?
( check your power management. I'm betting one of the monitors is going to sleep and pre 11.10 you need dummy plugs or a live monitor at all times or the card turns off )
no, :| but im really not in any mood to change my 11.6/2.5 to 12.1/2.1 Ugghh, It's such a headache