E60 Central Locking failed on one door only

[donkeydavid]

The other day a passenger in my 2008 E60 tried to open his door at the same time as I pressed the unlock button on the dash. He was in the front passenger seat but strangely the rear offside central locking then wouldn't work. The door could only be opened by using the handle on the inside and locked by pressing down the button and closing the door. At the weekend, I had to open the locked door so stretched behind from the driver's door and tried to pull the handle - I have a feeling I pressed the lock or unlock button on the fob at the same time and this seems to have knackered it completely. Now the door won't open at all - pull the handle on the inside and the button comes up but the door won't open. Release the handle and the button goes back down. What have I done? All the fuses are OK and the locking on all other doors and boot are OK.