Help with Standard AU Radio Code

[dinga]

Have an issue with the standard AU1 Radio in my work ute.

To cut a long story,

1. Replaced battery
2. Thought I remembered the security code for the radio.
3. Thought I knew it 4 or 5 times.
4. Pucked it up 4 or 5 times.
5. Now the radio will not let me enter the code. Flashes "Err".
6. Disconnected battery for approx 1 minute.
7. Still will not let me enter the code.

Can someone please tell me how I can fix this. I am sick of hearing my own voice trying to sing!!!!!

Thanks heaps
Darren