Error Code 43 on Vista

OS: Vista Ultimate x64
GFX: 2x Asus 8800GTX
MB: Asus Striker Extreme with BIOS v.1002

Hi my problem is really bugging me.

Error: This System was running fine but a few days ago the Gfxcard in
the PCIEX16_1 slot stopped loading the driver and in device manager it
is yellow with an error code 43. The Gfx in PCIEX16_3 runs fine, I
even tried running them individually but the one in PCIEX16_1 always
reports an error code 43.
Could it have sth to do with the Beta BIOS v1002? But in the ASUS
forum nobody reported having problems after updating so...

Any suggestions? I really dont want to RMA.
If you need more info just ask.

Alex Griffin