Weird problem - serial number won't stick

I just bought LNS today. The software won't stay validated for more than a few reboots and it's driving me crazy.

The weird thing is that if I write an image of my system partition to another partition on the same drive or on another drive, it will stay validated. I don't understand what could be causing this.

I zeroed out my drive and did a fresh reinstall of Windows XP as the most drastic step to eliminate as many variables as possible, and it still won't stay registered on the intended partition. I simply reboot a couple of times, and sure enough, the greyed out box becomes blank again. It doesn't happen on any other partition on my three drives that I tested, but I don't want my OS on those other partitions.

I really need help to figure out what's going on!