Cause : Modbus TCP over comes when the Master communication value exceeds the allowable number of the communication cards. This warning comes when connection occupied due to not disconnecting the Modbus TPC while the upper unit is connected without communicating.

1. Decrease the Master communication value.
2. Revise the program of the upper unit to disconnect the connection while the communication is not used for a long time.
3. Revise the program of the upper unit to use the same Modbus TCP connection when connecting to the same communication card.