As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE OPERATING THE APU DURING CRUISE FLIGHT WITH THE LEFT GENERATOR PLACARDED INOPERATIVE, THE APU GENERATOR TRIPPED OFF. THE FAILURE WAS ACCOMPANIED BY AN AC CROSSTIE LOCKOUT LIGHT. THE APU GENERATOR WAS RESET AND POWER WAS RESTORED. MAINTENANCE REMOVED AND REPLACED THE APU GENERATOR CONTROL UNIT PER MM 24-20-07 AND OPERATION CHECKED GOOD. PART TOTAL CYCLES, 14,523.