What was found
ON CLIMBOUT APPROACHING LEVEL OFF ALTITUDE (PASSING FL 330) EICAS MAIN CARGO DOOR DISPLAYED. PRESSURIZATION WAS NORMAL, DIFFERENTIAL PRESSURE WAS SHOWING APPROX. 8.3 PSID WHEN EICAS DISPLAYED. COMPLIED WITH QRH & DESCENDED TO 10,000'. MAIN CARGO EICAS NO LONGER DISPLAYED PASSING APPROX 13,000' AND DIFFERENTIAL CABIN PRESSURE ALMOST AT ZERO. DESCENDED AT 270 KIAS & SPEED OF 250 KIAS AFTER LEVEL OFF AT 10,000'. AFTER BLOCK-IN CONFIRMED MCD WAS FAIRED, VENT DOORS WERE CLOSED & FAIRED, & DOOR LATCH STRIPES ON LATCH CAMS WERE IN FULL VIEW OF ALIGNMENT MARKS. ADJUSTED SWITCH S896.