Rear passenger door won't lock on 2003 Mercedes-Benz ML500

I have a 2003 ML500 and the rear passenger door won't lock manually or with the remote. It makes like three clicking sound when you use the remote to try to lock it. All the other doors works just fine. Please help!

1 answer
The inner door trim panel would have to be removed to see the linkages are operating correctly, most likely the lock actuator is bad.