Is it an 11 digit code, or an 12? If it's a twelve digit code, have you tried turning caps lock on before entering it?
Edit: Okay, so I even now got an 11 digit code to work...
I typed in the 11 digit code, and tried to guess the 12'th digit after it. As it may have failed to print on the sticker. And I actually got it to work. First do as I said above, make sure caps lock is on and enter your code. If it is 11 digits, then add an extra digit to the end. Starting with 1, and if that doesn't work 2, 3, 4, 5, 6, 7, 8, 9, 0, move on to alphabet letters. Q, W, E, R, T, Y... Make sure caps lock is still on. I eventually guessed the right last digit. I guess there could be a chance your twelth digit was suppose to be in the beggining of your code, and you'll need to guess the number/letter before your code. Heck it could even be in the middle of your code somewhere, but for me it was at the end.
