As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLIGHT 5904 - MSY TO CLE. AFTER TAKEOFF, WHEN THE CREW ATTEMPTED TO RAISE THE LANDING GEAR LEVER BUT THE LEVER WOULD NOT MOVE TO THE UP POSITION, AND A LG AIR/GND FAIL MESSAGE WAS DISPLAYED ON EICAS. THE CREW CONFIRMED THAT THE AIRCRAFT WAS STILL IN GROUND MODE. THE APPROPRIATE CHECK LISTS WERE FOLLOWED AND THE AIRCRAFT LANDED BACK AT MSY WITHOUT INCIDENT. THE AIRCRAFT WAS FERRIED TO CMH WITH THE LANDING GEAR LOCKED DOWN, BUT HAD TO DIVERT TO KBNA DUE TO INCREASED FUEL BURN. IN KBNA MAINTENANCE FOUND CMC MESSAGES FOR LGEU FAIL AND THE LGEU WAS REPLACED. THE PROX SYSTEM OPS CHECKED GOOD AND THE AIRCRAFT WAS RELEASED TO SERVICE.