Gary,
All very odd if everything’s been working up until now. It sounds as though the remotes are transmitting OK, and I assume that the keys open the bonnet and boot?
I don’t know if this Rennlist 996 post will help, but could be worth a try (shared electronics with the 986):
I had the same problem with both of my keys. I tried the "trick" of holding down the lock button for six seconds after manually unlocking the door to "resync" the key with the car. No dice. I ended up taking it to Porsche out here in Santa Clara and was told that those 996 keys have circuit boards that go bad after about 10 years. Sometimes the light will still turn on when you press the buttons, but the car will never respond no matter what you do. The temporary solution was to remember that you turn left to unlock, turn right to lock when you are manually opening the door. If you do the reverse the alarm will go off. When you get the door open you have to start the car within 10 seconds or the alarm will go off. This is because the car needs to "read" the key when it is unlocked manually or it assumes it was jacked.
Jeff
