As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON ENGINE START, MAIN CARGO DOOR LIGHT & HORN SOUNDED. CREW RETURNED TO THE GATE (BTB). MTC FOUND MAIN DECK CARGO DOOR CLOSED BUT NOT LOCKED. CLOSED AND LOCKED MAIN DECK CARGO DOOR IAW AMM 52-32-00. DOOR CLOSED & LOCKED PROPERLY. ACFT RETURNED TO SERVICE.