As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT 7790, YOW TO IAD. AFTER TAKEOFF THE FLIGHT CREW RECEIVED A LG AIR/GRND FAIL MESSAGE ON EICAS AND THE LANDING GEAR WOULD NOT RETRACT. THE AIRCRAFT RETURNED TO YOW AND LANDED WITHOUT INCIDENT. MAINTENANCE CHECKED THE CMC FOR MESSAGES AND FOUND A PROX SWITCH FAIL CMC MESSAGE. THROUGH FURTHER TROUBLESHOOTING THE NOSE LANDING GEAR WEIGHT ON WHEELS PROX SWITCH WAS FOUND TO BE AT FAULT. THE PROX SWITCH WAS REPLACED AND THE SYSTEM OPERATED NORMALLY.