immobilizer problem

I’m having problems starting my Swedish sold 88 GTI. I have replaced the battery and done some checks on the ignition & fuel delivery system, which is all OK. So now I’m thinking it could be an immobilizer problem. When I bought the car the immobilizer was deactivated and I have never attempted to use it. I have the 7 digit code but this doesn’t seem to work and I’m not sure if I am entering the code in the right way.
There is a small red LED on the keypad which remains red after I enter the code.
Here is a picture of the unit:
http://asasoderen.web.surftown.se/images/Imob.jpg

Is there a re-set code for the unit?

What is the procedure for entering the code? Do I just enter the code or do I need to press a button to confirm after the 7th digit is entered?

Any help would be much appreciated!