Check list

Is the COM port in use by another application or are the settings incorrect?

Is the device (PLC) that you are trying to communicate with connected to the power supply?

Is the cable between PLC and PC/IPC connected correctly?

Do the used addresses exist in the PLC ?

Have you analyzed the log file with the log viewer (which errors have occured)?

When using communication via TCP: make sure the configured port is free and not blocked by a firewall. ? Test with telnet: can you establish a connection?