As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF, CREW NOTICED AIRCRAFT WAS NOT PRESSURIZING AND LEVELED OFF WHEN CABIN ALTITUDE CAUTION MESSAGE RECEIVED. MANUAL MODE WOULD NOT CONTROL CABIN. CREW RETURNED TO FIELD AND LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTED AND FOUND AFT CARGO DOOR INCORRECTLY CLOSED. MAINTENANCE CYCLED AND CORRECTLY SECURED DOOR IAW AMM. PRESSURIZATION CHECK WAS GOOD. ACFT RELEASED FOR SERVICE.