As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
UPON RETURN TO AIRCRAFT THE COCKPIT DOOR WAS CLOSED. ATTEMPTED TO GAIN ACCESS USING EMERGENCY PROCEDURES, FLIGHT CREW ENTERED CODE SEVERAL TIMES TO GAIN ENTRY TO CONTROL CABIN, NO HELP. HAD TO SHUT OFF APU USING FIRE HANDLE. FLT CREW TRIED 2 TIMES TO OPEN DOOR WITH CODES AFTER ENTRY WAS GAINED. FLT CREW COULD NOT OPEN DOOR AFTER ENTRY WAS GAINED, DF0237 MEL 5251C.