As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT NR 2375 - DEPARTING DEN WAS UNABLE TO PRESSURIZE. AIRCRAFT RETURNED TO DEN WHERE GP EXPRESS MAINTENANCE DEFERRED THE PRESSURIZATION SYSTEM. LATER THAT DAY GP EXPRESS MAINTENANCE FOUND THE INSPECTION WINDOW FOR THE AFT CARGO DOOR LOCK MECHANISM BROKEN. WINDOW WAS REPLACED AND SYSTEM CHECKED SATISFACTORY. AIRCRAFT WAS RETURNED TO SERVICE.