That is very strange. Once it validates it is good until you make some major hardware change. My guess is the error is on your part but, in any case, you should be able to validate and register online or by phone. Whenever I have had trouble online I have used the phone and it has worked 100%.
And I say this as someone who is still using Win XP SP3 and going through a lot of effort to learn me some Linux for the day when XP dies.