What was found
FLIGHT 2885, CREW REPORTED DURING CLIMB THROUGH 10,000 FT, RECEIVED AN EICAS WARNING MESSAGE AND CABIN ALTITUDE ABOVE 10,000FT. PERFORMED AOM PROCEDURE BUT ACFT WOULDN'T PRESSURIZE IN MANUAL MODE. DECLARED AN EMERGENCY AND ELECTED TO RETURN TO DEPARTURE. AIRCRAFT WAS REMOVED FROM SERVICE. REMOVED AND REPLACED GROUND CONNECTION VALVE IAW AMM 21-22-04. PERFORMED PRESSURIZATION IN MANUAL AND AUTO, OPS CHECKED GOOD IAW AMM 21-31-00.