Like I said to you earlier if the other key works it could be the battery in the key, or the key has got out of sync somehow, try new battery first.. or I think this applies across the Audi model range..
http://www.ebay.co.uk/gds/How-To-Pro...0293524/g.html
unlikely I guess given your spare key works but this thread from Ranj describes what happens if the wire is suspect..
http://forum.a8parts.co.uk/showthrea...ht=immobiliser
now get back to packing
