What was found
(B-18716) DURING CRUISE, CABIN ALT RAPID RISE, FOLLOW QRH PERFORM EMERGENCY DECENT, DUMP FUEL AND RETURN TO TPE AT 0605L. ACFT AFTER REACHING CRUISE ALT(FL300) SEVERAL MINUTES "CABIN ALT" WARNING APPEARED WITH WARNING SOUND (WARNING WILL TRIGGER WHEN CBN ALTITUDE LESS THAN 10,000 FT). CREW FOLLOW QRH-CABIN ALTITUDE, CABIN DEPRESSURIZATION, CONFIRMED: ALL PACKS-ON AND OUTFLOW VALVE LESS THAN CLOSED, IN AUTO MODE. FOLLOW QRH PROCEDURE PERFORMED EMERGENCY DECENT DUE TO CABIN ALTITUDE WAS STILL CLIMBING, DURING INITIAL DECENT CABIN ALTITUDE WAS STILL ABOVE 10,000FT, UNTIL CLOSE TO FL 100. ASC AND CAA HAD INTERVENED FOR EVENT INVESTIGATING. TROUBLESHOOTING IS IN PROGRESS.