As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) AFTER TAKEOFF, A MASTER WARNING LIGHT WENT ON INDICATING THE FUSELAGE DOOR, 2R SERVICE DOOR, AJAR. THE ACFT CLIMBED TO SID ALTITUDE OF 5,000 FT AND NOTIFIED ATC. THE CHECKLIST FOR THIS WARNING WAS COMPLETED AND THEN THE DECISION WAS MADE BY THE FLIGHT CREW TO RETURN TO POINT OF DEPARTURE. IT WAS AN UNEVENTFUL LANDING AND UPON ARRIVAL, MAINTENANCE TOOK OVER. MAINTENANCE CONDUCTED AN INSPECTION OF THE ACFT AND FOUND A FAILING PROXIMITY SENSOR.