Decoding blaupunkt nissan 7646340318 radio?

[Dannywhite]

I have recently bought a radio/cassette unit for my 2001 Micra. It came with the code. when I installed the unit, I input the code, and the radio said "secure". I tried again, and now it doesn't ask for a code. I have the unlocking code (bought from radio-codes.co.uk last night) but it won't let me input it. How do I proceed?

Thanks for your help in advance.