Hi guys,
I wanted to share a cheap solution to this issue. I recently bought a MY07 Spec.B, and at the time of picking up the car the owner said that the second key needed a new battery... silly me for believing. Long story short - there was no transponder chip in it.
I didn't want to spend the $375 Subaru quoted for a new key as they wont sell the chip by itself and i already had a key cut with working remote. I couldn't get any auto electricians to touch it either.
After much research, the chip I needed was a 4D-62, found one on Ebay in Hong Kong. $15 including postage, fitted it this morning and took the key to Subaru who have now re-programmed it for free.
For those who are interested the seller was newkeys2010
Very happy, and saved $360!