Some folks that have bought
Command & Conquer: Red Alert 3 seem to be missing the last letter or number from their serial number. If you find out you are missing the 20th character, EA
suggests you try guessing. You'll eventually get it right seeing as it can only be A-Z or 1-9. Another way is to contact them and attach an image of the offending serial number. It might be faster though if you just tried and guess and it's not like passwords where you get locked out after a certain number of tries.