Immobiliser not working

I have a 2003 Subaru Heritage Wagon (Liberty body) and the buttons on my key remote lock and immobiliser have stopped working. I changed the battery and checked that it was delivering 3V. Also, I cleaned the small circuit board with alcohol and checked that the contact points were all ok. Fortunately the dealer supplied a spare key when I bought the car and it works just fine, but I'm worried that if the spare also fails I'll be left high and dry. Another thread about a Scenic mentioned about the 4 digit code from the manufacturer to reset the key. I've got my code but I don't think that resetting it will make both keys work. If you have any suggestions regarding repair of the key or advice about a replacement.. I would be much obliged.

BillyBoy

Problem solved. I took the functioning and non-functioning key/remotes to a locksmith. They had a machine to test whether a radio signal was being emitted from the key when the lock/unlock key was pressed. The faulty key wasn't generating a signal. Although I cleaned the terminals on the small chipboard inside the key, the locksmith scraped some more and then the key started working.