Have you tried raiseing your PCI Express clocks above there default "Auto" or "100" setting?
I have no experience with this actual board myself but I'm still very tempted to choose it as my next board when I move onto SLi and add a second 7800 GTX.
As the others have said, it seems that this board can't cope with FSB's higher than 235. That may explain why you're having a broblem with your 955 EE as it's default is 266 or 266.5.
I've just had a browse through previous posts and sure enough, there are a few posts from people with problems raising their FSB's over 235 or 240.
Aside from raising the PCI Express frequency all I can suggest is try different motherboard BIOS's. Though right now I'm thinking that adjusting the PCI Express clock is the most lily to work.
I have my Pentium 4 650 (FSB200) overclocked to 4.0GHz (FSB235) and I currently have my PCI Express frequency set to 115. I expect that you may need to set yours to somewhere around 120 or 130.