Check list

Is the COM port in use by another application or are the settings incorrect?
Is the PLC that you are trying to communicate with connected to the power supply?
Is the cable between PLC and PC/IPC connected correctly?
Is the option "CRC" activated in the communication monitoring of the PLC?
Do the lists, which are queried as zenon variables, exist in the PLC?
Did you enter all user-defined lists that the driver is supposed to query in the driver configuration?
Did you configure different variable types for one PLC data list? See chapter "Limitations"
Did you define variables in zenon that have no address in the PLC?
This should be checked with the standard lists 0-8. E.g. Integer List N7 addressable up to offset 100 (default).
Have you analyzed the "driver communication error file" (which errors have occured)?

In case of communication problems, the driver writes a detailed problem analysis into the driver communication error file. This file is stored in the project directory (RT\\FILES\\zenOn\\custom\\log). The name of the file is _<drivername>.TXT.
The file can be opened with any text editor, e.g. Notepad.

For additional error analyses, please send a project backup and the "error file" to the support team responsible for you.