Either that, or you're not entering the number correctly, especially if you printed it out. Problem is, the font they use to show you the number for printing is REALLY hard to read. 0's look like D's and 5's look like S's... among other things. You really have to scrutinize the font characters.
When I installed the game at work, and then brought it home and tried to input my MP code it took me about 5 tries to really get every digit in there correctly. Really bad design move, it should print out in basic Arial or Courier.
So you might have either copied it down wrong from the original installation, or are inputting it wrong into the new installation... or both
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The only thing I like more than pie is having more pie than I'd like.