I had a similar issue before sometimes its a stability issue, remember its basically a stress test, My card was Overclocked and i backed it off and it ran ok.
Another time i had the same thing and i installed 3dm and downloaded it again, installed it and it ran fine.
So you can either re-download and install 3dm or try down clocking your card and seeing if it runs then. If it does run 3dm after a down clock i would get in contact with His and tell them.
I would try uninstalling and deleting ,then re-downloading 3dm amd reinstalling it first.
But for the purposes of testing if the card is unstable you would be looking to down clock the card to referance clocks which i beleive are, 625 engine clock and 1986 on the memory. personally i would round it down to1980.
Download the free version from the net, it makes more sense now you say its a PC Format Disc i have loads of them and lots of flaky app that either wont run properly or don't install properly. To be honest i stopped buying it as i find more up to date info on the forum.
http://www.futuremark.com/
What error are you getting? I was getting a "DXT texture format" error in 3dmark06 with my 4870x2, but then I just had to set it to support dxt textures under "DirectX settings" in Catalyst.
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