As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT LEVEL 250 AMBER CABIN ALTITUDE ILLUMINATED ON EICAS. CABIN ALTITUDE WAS AT 8500 WITH A DIFFERENTIAL OF 4.0. AFTER DONNING OUR OXYGEN MASKS RED CABIN ALTITUDE AND ILLUMINATED AND WE HEARD THE DOOR SEAL (MAIN CABIN DOOR) POPPING AND HISSING. AN EMERGENCY DESCENT WAS INITIATED TO 8000FT. CABIN PRESSURIZATION WAS INOPERATIVE. TROUBLESHOOTING LED TO A FAULTY GEN I/O CARD.