Please make sure you are typing in the registration code. It is pretty common to accidentally type in the product # or order #. Scan down your order email to the line that says "Your registration code is: " and the number right after that is your registration code!
Also, make sure that you've...
Do not panic! In many cases, there may be a processing delay. Sometimes, people have supplied the wrong email address. In rare cases, the registered users are unreachable due to mis-configured email clients, spam filters or privacy control.
Read this for more info.