This may be due to one of the following reasons:
1.Incorrect name and/or unlock code
Make sure that the name and unlock code is typed exactly as shown in your original e-mail. Pay particular attention to spaces and capital letters. Also try to actually type it in instead of cutting and pasting. On some computers we have found that pasting adds some hidden characters.
2.When typing in the numbers, don't use the number keypad off to the right of your keyboard, because they are sometimes interpreted as different characters and it will not be accepted, although it may look right to you.