As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB OUT, AT APPROX 8,000FT, THE CREW RECEIVED AN OXY LO PRESS EICAS MESSAGE. THE CREW O2 INDICATED ZERO PSI ON THE MFD. THE ACFT LEVELED AT 10,000 FT AND IT WAS DECIDED TO RETURN TO DEPARTURE. THE CREW OXYGEN SYS WAS PLACED ON MEL AND THE ACFT DEPARTED WITHOUT INCIDENT. CREW OXYGEN SYSTEM MEL WAS CLEARED BY REPLACING THE OXYGEN ALTITUDE SENSING SWITCH IAW AMM 35-20-03 AND THE SYSTEM OPS CHECKED GOOD.