I just purchased a 1999 Boxster. The door locks work fine with the key and the dash toggle switch. However the key lock swicth on neither of the keys works, and both have fresh batteries and I can see the LED turn on when I press a button. I know that the battery has been drained at some time before I bought it and I have removed the battery to run some new radio wiring.
From searching online it looks like there is a system in the car to pair the keys and car. I tried one process I found to unlock car, turn on ignition, turn off ignition, hit lock key. No joy.