Hi jschulze,Hello, and welcome to the forums!
In order to provide helpful recommendations, we're going to need more details.
What device or equipment is generating this error?
Are there additional details included with this error, perhaps found in a log file, or similar? For example, is the IP address that failed to ping included somewhere?
Do you know which specific device is the "Modbus TCP communication gateway"? If so, can you ping the device from a laptop connected to the network (and configured on the same subnet)? Can you confirm the IP address of the Modbus TCP communication gateway matches the IP address of the device or equipment that's generating the error?
Is this a new installation or was this system running successfully for a while? If it's the latter, has anything changed (configuration settings, new devices added to the network, etc.)?