Had same error upgrading from Vista Ultimate 64 to Windows 7 Ultimate 64, it was persistant and reading around the forums someone was suggesting it might be a memory contention issue. I had two pairs of memory sticks installed so i removed the ones from slot 2 tried agian and it worked first time. As this was the only change I made I figure this was the cause of my problem. After installation put the other two sticks back in and no problems - well none I can blame on Windows 7!!!