Radio Security Code Error all the time

Can anyone help with loading the security code. I have the code but the Radio display now always shows 'Err'. I originally got the 'Code' display when the battery was replaced. But, since I loaded the wrong code a couple of times, I now keep getting that darn 'Err'. I did leave it overnight & tried this morning 0 no good. Tonight, I disconnected the battery for varying periods up to 30 minutes & tried again but still no go. Do I just wait for another 24 hours or what? Otherwise I will have to go to a dealer !! (The AU has the "Prestige audio System")
Thanks in anticipation.. :