central locking faulty rover 75 x plate 2000 v6?

Hello
yesterday my central locking started playing up
the drivers door lock is playing up,
my key thob will lock all four doors,to unlock you should push the button once to open drivers door but nothing happens push the button a second time and the other three doors unlock, the drivers door stays locked.You can unlock the door using the key, and you can also open the door from inside using the handle
any ideas
regards derek