I am have the same problem on 6 new Dell Vostro laptops running Windows 7. We downloaded and installed Medialab 2008.1.33 between March 3-10, 2010. Study includes a DirectRT segment, but the error occurs in Medialab at the same place every time (~150 items in). Each individual questionnaire runs fine, it's only when I put several questionnaires together. The study also runs fine if I remove one of the longer questionnaires. Let me know if you need more info.