I had the same problem with mine, it's a nightmare! WD40 worked with me and has been fine ever since, from what i've heard it is a fairly common problem. Something in one of the locks gets stuck (mine was the passenger door) and because the one lock won't work, the central locking won't let you lock the rest of the car. It must just be dirt and grime that's worked it's way into the lock and because the key is rarely used it eventually sticks the parts of the lock together. Give the WD40 a generous squirt in every lock, then one by one go to every lock with the key and lock then unlock over and over again. Good luck!