As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
SHORTLY AFTER TAKEOFF, THE MAIN CABIN DOOR UNLOCK LIGHT CAME ON, CHECKLIST WAS FOLLOWED & THE PILOT ELECTED TO RETURN TO BLOCK. THEY LANDED WITHOUT INCIDENT. THE DOOR ALONG WITH LATCHING SYS WERE INSPECTED BY AN A & P. THE SYS WAS OPERATIONALLY CHECKED & THE DETERMINATION WAS THAT THE DOOR WAS NOT LATCHED AGGRESSIVELY ENOUGH TO COMPLETE THE LOCK MECHANISM FROM THE BEGINNING. NO OTHER DEFECT NOTED.