Guys, girls

Was assisting a fellow forum member long into the night. We were trying to match his remote keys to the second hand CCU he had fitted, as the car suffered from water ingress.

In the memory positions, the code is "1100" which shows two keys assigned to memory. However, he has only one key, and when the value is changed (test and save) channel 21 in address 46 central convenience reports an error. It does this regardless of what memory position you assign the key to.

There are no fault codes regarding the CCU or key programming at all.

The car is a Y reg Audi A4 (B6) 2.0.

I'm running fully registered 409.1 VAG-COM.
Help is hugely appreciated!
Paul