[jotoole]

Guys-
Bear with me a few minutes, I've reactivated key fobs several times, but I didn't take notes. One of these methods works, none do any harm.
Put your good (fob) key in ignition and turn right one click to activate accessories. Leave it in that position and close door, MAKE SURE key w/bad fob is in your hand!
Press and keep pressed the key fob button for the door locks and insert key into door lock keeping button pressed. Turn key in door lock as as you were locking then unlocking door 2 times, keeping button pressed. Release button and remove key. Manually unlock door and remove good key from ignition. Now shut door and see if fob works. If not, try various combinations of routine. e.g. unlock and then lock door 2 times. There are only so many variations on the theme. I just can never remember which. Within the last hour I reactivated my key using one of the combinations within 3 minutes.
I have to reactivate one of my keys every 6 weeks or so for this reason: When I drive my Boxster, I have Boxster key only, no other keys, in the ignition to minimize load on ignition switch. I use the Boxster key on my key ring, which carries all the other car keys, house keys, etc... to unlock my cars because I just about always have to have move cars around to get to the Boxster. Therefore my single Box key fobs rarely used to unlock. After 5 weeks or so, I have to reactivate fob buttons.
More info on Renntech.org. Search "remote key transmitter fix."