As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) WITH AN AIRCRAFT MECHANIC AND 2 FLIGHT ATTENDANTS ON BOARD, THE REAR SERVICE DOOR OPEN WARNING LIGHT CAME ON AT 14,000 FEET. AIRCRAFT DEPRESSURIZE AND RETURN TO DEPARTURE. INVESTIGATION REVEALED THAT LOWER REAR HOOK WAS NOT GOING IN PLACE PROPERLY, DOOR WAS RE-RIGGED IAW MM FIG. 3.2.103. AIRCRAFT RETURN TO SERVICE.