Will the rear doors unlock/lock from their own switches? You mentioned manually, not sure if you ment to both physical and electronic control of the rear doors.
First - double check that the child safety interlocks are not switched on the rear doors.
Secondly, need to visually inspect that the wiring running to the rear doors look OK, if they look fine, you'll need to pull the interior door panels off on the doors to see if there is power running to the switch. Need to check the master control switch as well.
Likely that either the connection on the bottom of the master switch is bad or the wiring running to the rear doors is broken.