As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE, CABIN ALTITUDE WARNING DISPLAYED. UNABLE TO CONTROL CABIN ALTITUDE WITH AUTO OR MANUAL CONTROL. CREW DECLARED AN EMERGENCY AND DESCENDED TO 10,000 FEET. THE FLIGHT RETURNED TO MSP AND LANDED WITHOUT INCIDENT. MAINTENANCE FOUND THE LEFT HAND PACK INOPERABLE. REMOVED AND REPLACED THE COOLING TURBINE, OPERATIONALLY CHECKED THE SYSTEM AND RETURNED AIRCRAFT TO SERVICE.