As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
MKE FLIGHT 2560 - THE CREW REPORTED A AIR/GROUND FAIL MESSAGE ON TAKEOFF. THE AIRCRAFT RETURNED TO MKE AND LANDED WITHOUT INCIDENT. MAINTENANCE INSPECTED AND CLEANED DEBRIS FROM RIGHT MAIN LANDING GEAR PROXIMITY SWITCH. OPERATIONAL CHECKS WERE GOOD. THE AIRCRAFT WAS RELEASED FOR SERVICE.