Mitsubishi Electric MELSEC Q Series Reference Manual page 560

(b) When a programming tool connected station is faulty
Control station
No.1
Added station
Control Selected
station
station
No.4
558
Normal station
No.2
Normal station
No.3
Select the own station.
An error has occurred in the station No.4.
Click the error details button.
The Error Factor field indicates that a station other than the station No.4 has
been also set as the control station.
Take corrective actions according to the troubleshooting.