Help! Amd crossfire crash.

[SlasherNL]

Last weekend I build my second computer and i'm having a problem.
I have two radeon HD 6850 graphic cards and crossfired them.
If i start the computer, it starts windows and after a couple of second the screen goes to the infamous blue screen.
The computer restarts and starts to use the motherboards graphics.
I already tested the cards individually, and the both work.
Has someone a clue what's wrong?

My parts:
Sapphire hd 6850
Asus eah 6850
Amd fx6200 @3.80 ghz
Corsair gs 800W
10gb RAM
motherboard: Asus m5a97

 

[Todesengel]

Sapphire hd 6850
Asus eah 6850

It may be that since the cards are different manufature that they dont work together, even though they have the same specs otherwise and work by themselves.