As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ORD - FLT 104 - WHILE EN ROUTE SEA/PHL, CREW RECEIVED THE EICAS MESSAGE 'R GEN DRIVE.' APU GENERATOR WAS ON MEL. FLIGHT DIVERTED TO ORD AND LANDED WITH NO FURTHER INCIDENT. MAINTENANCE REPLACED THE RIGHT IDG DUE TO A SHAFT FAILURE. (X)