As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: AN EMERGENCY WAS DECLARED DUE TO: CLIMBING THROUGH APPROXIMATELY FLIGHT LEVEL 8,000 WE NOTICED PRESSURIZATION MODE SELECTOR WAS IN MANUAL THEN WE SELECTED AUTO, AT 10,000 FLIGHT LEVEL WE GOT CABIN ALTITUDE LIGHT WITH ACCOMPANYING HORN. SOME PASSENGERS AND CREW EXPERIENCED BLOODY NOSES AND EAR ACHES. AIRCRAFT AIR INTERRUPTED BACK TO AND LANDED SAFELY AT ORD. ACCOMPLISHED FIM 21-31-00 NO FAULTS NOTED ON EITHER CONTROLLER.