We're working with a reviewer who had a similar problem with the review copy (a standalone version of the game, not in GameTap). Would you be able to send us a copy of your DXDiag info? Comparing it to hers will let our tech guys figure out what your systems have in common and might help them resolve the problem.
To do this:
-Go to Run
-Click Save all Information
You can email the file to us at firstname.lastname@example.org