I had to replace my battery recently and now my radio wants a code. I have the original papers for the car and the code card but it won't accept the code. Am I doing something wrong???

I have a '96 E300D and I presume it has the Alpine radio since it has the CD changer controls on it (I just bought the car used).

Here is what I've done so far:

1. At the CODE prompt I enter the 5-digit code
2. I press the SC button (I've also tried TUNE)
3. Radio goes back to CODE


Now I have to wait 10 minutes to try again and I've tried it 3 times already. Any Tips???