What was found
AFTER TAKEOFF, CARGO DOOR LIGHT CAME ON AND AIRCRAFT WOULD NOT PRESSURIZE. RETURNED TO LAX. *S/D* CARGO DOOR HANDLE FLAP ASSY (P/N D5237130200000) DID NOT FULLY ENGAGE LOCK PIN ON HANDLE ASSEMBLY. VIBRATION CAUSED BY TAKEOFF RESULTED IN MOVEMENT OF HANDLE OUTBOARD AND CONSEQUENT ACTIVATION OF VENT FLAP ON CARGO DOOR. AIRCRAFT WOULD NOT PRESURIZE WITH VENT FLAP OPEN. MAINTENANCE ADJUSTED HANDLE FLAP, VENT DOOR AND PROXIMITY SENSOR PER AIRBUS MM. NO OTHER FAULTS NOTED.