I'm afraid some security feature embedded in Win7 didn't really appreciate the bootscan

I don't have this problem as it's not available yet for W7/64 (the boot scan), but good to know it can generate such an issue, and thanks for posting

... now if your activation files got corrupted, that's another story. If you're running a legit version of Win7, you can always try to repair the activation files by validating Windows:
http://www.microsoft.com/Genuine/ If your system is OK now, you don't need to do it. Would still be better, just to make sure everything is OK. Now if you're not running a legit version of Windows (which I don't assume, since you got a Dell and probably acquired 7 with it), be aware that this new W7 validation check will change your life in Windows, just a warning, but again, I don't think you're concerned)