BMW Repair: Security Radio Op, good shape, card id

Question
Just bought my wife her 'dream car', a 1987 528e.  The car is in pretty good shape, though the automatic antenna is broken.  I have the original 'code card', and the instruction manual for the radio, but try as I might I cannot get it to do anything but show the word 'COdE' to me and beep on the 4th of the 5 number code. Is there a trick to this like disconnecting the battery, or could the code from the card possibly be changed...? Any advice would be greatly appreciated- Hate to go to a dealer and look like an idiot...Thanks.

Answer
I think that this stereo has a memory; meaning that if you attempt the code 3 times then it requires you to disconnect it from power for 1-2 hours or must remain on for 30 minutes before it will reset itself.  You may have the wrong code.  Goto the dealer with your code card, ID and title and tell them it's not working and see if their database matches your card.  If it does, than the radio was probably replaced and requires a different code, the radio will then need to be pulled out to get the serial number.
-cheers