As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT 7794, YYZ TO IAD. AFTER TAKEOFF WHEN THE LANDING GEAR WAS SELECTED TO UP THE FLIGHT CREW RECEIVED A LANDING GEAR AIR/GROUND FAIL MESSAGE ON EICAS AND THE LANDING GEAR WOULD NOT RETRACT. THE QRH WAS FOLLOWED AND THE AIRCRAFT RETURNED TO YYZ AND LANDED WITHOUT INCIDENT. MAINTENANCE CLEANED AND INSPECTED ALL OF THE MAIN LANDING GEAR PROX SWITCHES, RESET POWER AND THE SYSTEM OPS CHECKED GOOD.