CA only working with one fob

[Nanniepoo]

New to the forum as of a week ago. Just picked up an '08 X5 4.8i.

It has comfort access, but only appears to be working with one fob. Car will start, and doors unlock by touch properly with one fob, but not the other. I changed the battery on the second one, and it will unlock/lock the doors via the buttons, but no luck through CA.

I haven't tested starting the car, with or without it inserted, as the other fob was always with us.

Is there a physical difference between fobs? Is it possible that there was only fob that works with CA? Any way to register this as a CA key without going to the dealer? I'm currently doing research on getting set up for DIS/GT1/INPA...it's a lot to process.