As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AFTER TAKEOFF AND DURING CLIMB THROUGH APPROXIMATELY 11,500 FEET. RED CABIN ALTITUDE LIGHT ILLUMINATED. FOLLOWED QRH BUT CABIN ALTITUDE COULD NOT BE CONTROLLED. AIRCRAFT COMPLETED AIR TURNBACK AND GROUNDED BY MAINTENANCE. FORWARD LOWER CARGO DOOR WAS FOUND NOT TO BE CLOSED. MAINTENANCE CLOSED DOOR AND AIRCRAFT WAS RELEASED.