W140 central lock problelm

[mjgotts]

I have a 95 S320 that won't lock the passenger's side front door when the central lock feature is activated on the driver's side with either the remote, a key, or the dash button. I can lock the passenger door manually from the inside by pushing down the knob . It will unlock using the key in the passenger door but not the dash button. Any thoughts as to why and how this is repaired?