Why can't you lock the doors manually? If the remote dies (usually from a flat battery, or water ingress into the fob) putting the key into the lock and turning should either lock just that door, or all the doors.
If it locks just that door, it suggests a CL fault with the car itself. Could be a fuse. If if only one lock locks the car (eg drivers lock locks only drivers door, passenger lock locks the whole car) then it's probably an actuator in that door.
If manually locking the door locks the whole car, then it's probably the fob at fault. Get the dealer to change the battery and reprogram the system to use the keyfob (as if it's dead, it's probably been 'forgotten' by the ECU.
If you really can't lock it manually, as in the key won't turn, then I'd suggest it's the actual lock that is physically at fault. The other door locks should work though.
Chris
April 2007