One door won't open or close with KeyFob

[thefork]

The passenger side rear door will no longer lock or unlock via the keyless remote. All of the other doors work fine. If I sit there and keep trying it it will sometimes unlock the rear passenger door, but not often.

Any ideas on what is wrong and how I can fix it?

[new echo owner]

Door lock actuator will be my guess. The right front and both rear doors are controlled by the same circuit.

N.E.O.