If it's a slot-loading iMac then if you open up the bottom where the memory goes you will see a little reset button. If the computer is on it's screen then when you look inside it will be to the left and down a little. If you hold this button in for about 5 seconds it will reset the...
I have 2 copies of Mac OS X Server and both of them were missing a single letter at the very end of the registration. The example on the screen where you enter the number should show you. I just went through the alphabet until i found the right letter.
