Hi Underdog,
I've got a 200tdi (yes i know, before i get jumped on, its a completely different system) with a 1 button remote that worked absolutely fine for the first 16 years of its life then with not apparent warning decided to give me the complete run around. there was no end of insanely annoying faults ocurring in a completely unpredictable manner, from false activations, to not unlocking, to not locking to the immobiliser staying on. all these problems developed really quickly after the 1st fault reared its head. only a new alarm module solved the problem (on my truck it was behind the steering column to the left of the fuse box however something leads me to believe that yours is in a kickplate somewhere?, someone on here will know) and now a 17 YO disco is now very well behaved again. what i'm trying to say is that there maybe much more knowledgable people out there that can correctly diagnose your module fault or maybe even fix it for you when in my honest opinion and it is just my opinion that £20 quid on e-blag for a new (secondhand) module and a set of programing instructions from on here somewhere will cure your fault and save much time and headbanging. i did it £5 plus £1.99 postage for my AMR 2103, after weeks of typing,phonecalls and pulling my hair out i so wished i'd done it sooner.
Goodluck.
p.s. the model number of your module is written on it, locate it, read it and google it, straight swap!.