They can loose their program, has happened to me a few times, it's quite simple to re-program.

Radio Frequency Programming Instructions:

• Insert the ignition key and turn from position II (Ignition) to position 0 (All off) and back four times within three seconds.
• Remove the ignition key. The locking control system is now in "learn mode" for the next 20 seconds and the red warning system LED (By the clock) stays on continuously to indicate this.
• During the 20 seconds press one of the transmitter buttons. The remotes signal and code number is learned by the locking module and is indicated by flashing the warning system LED.
• Wait until learn mode times out (20 seconds) or switch the ignition back to ON.