My six year old X-250 3 button remote control key fob was looking a bit tatty so, for less than a fiver, I bought a new plastic shell case which is identical to the original. I transferred the pcb, ignition blade and battery holder to the new shell. Going out to the van the remote operated the doors as before, but putting the key in the ignition the immobiliser light stayed on and the van wouldn't start. The spare key worked fine. Putting all the bits back in the original fob it worked perfectly. I'm at a loss to understand why this should be and if anyone has any ideas I'd be glad to hear from them!