I got everything working except one problem. I keep getting "Verification failed, check hardware!" on the 2nd GPU of my (bought used) 5970. I tried underclocking, even down to 560/1000 and it still does it very often. I swapped in a 2nd (bought used) 5970 and the same thing. It works, it just shows a lower khash rate and lots of errors. The whole time core 1 is happy not a single error on both cards.
What would cause this? Any ideas? I'm skeptical of used hardware, but the fact that both cards show the same behavior gives me hope its a config issue.
I'm running Ubuntu 10.10 with m0mchill poclbm. Motherboard is MSI-7599 AM3 spemron with 2 sticks of kingston 1gb pc1033 dd3 ram. Corsair 1200w gold psu. Motherboard is just sitting on workbench at this point until case gets here. I have DVI monitor plugged into lower dvi port of the card. Switching to top doesn't help.
Sounds to me like you have cross-fire is enabled; if that's the case - you need to turn it off by typing:
$ aticonfig --crossfire=off --adapter=all
Or, like bitjet suggested, you are using a wrong ATI Stream SDK (like 2.2 or 2.3).