I've just been called by an Audi mechanic who tells me to disconnect the battery again (negative) wait 2 mins (without keys in ignition) then try and reconnect it without causing a spike and the system should have reset. He says the code is only for the radio and my radio doesn't have a problem. I asked him how to reconnect without causing a spike and he said touch the connection back on the battery and if you see sparks disconnect and try again, after a couple of attempts it won't spark and all will be good. This sounds a little odd to me, but maybe worth a try.