As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
MAIN CARGO DOOR LIGHT CAME ON IN-FLIGHT; UNSCHEDULED LANDING MADE IN MEMPHIS. NR 4 MCD PIN BACKED OUT SLIGHTLY TO WHERE SWITCH WAS NOT ENGAGED. PERFORMED OPERATIONAL CHECK OF MAIN CARGO DOOR SIX TIMES; COULD NOT DUPLICATE PROBLEM. ALSO, CLOSED DOOR AND PRESSURIZED AIRCRAFT; OPS/SYS CHECKED NORMAL.