As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE FLIGHT, THE CREW REPORTED THAT THE CABIN PRESS WARNING LIGHT ILLUMINATED IN FLIGHT. NEITHER MANUAL OR AUTO MODES OF PRESSURIZATION WERE INOPERATIVE. DECLARED AN EMERGENCY AND RETURNED TO DEPARTURE. LANDED WITHOUT INCIDENT. R & R THE CABIN PRESSURE WARNING SWITCH. ALL OPS TEST PRODUCED SATISFACTORY RESULTS.