An error subsystem that Copter and Plane do not write

What ArduPilot says:

• ERR MAIN (Subsys 1)
• ERR OPTFLOW (Subsys 4)
• ERR FAILSAFE_GPS (Subsys 7)
• ERR AUTOTUNE (Subsys 14)
• ERR FAILSAFE_SENSORS (Subsys 26)
• ERR FAILSAFE_LEAK (Subsys 27)

These numbers are in ArduPilot's list of subsystems, but nothing in Copter or Plane 4.6 and 4.7 writes them: 1 MAIN, 4 OPTFLOW, 7 FAILSAFE_GPS, 14 AUTOTUNE. Numbers 26 FAILSAFE_SENSORS, 27 FAILSAFE_LEAK and 28 PILOT_INPUT belong to ArduSub, the firmware for underwater vehicles (depth sensor, water leak, lost pilot input). If one of them is in your log, the log comes from another vehicle type or from a much older firmware, where the numbers were used differently.