Hey Joe,
This is the error thrown when MATLAB cannot connect to the Moku:Go with the given IP address. You said you are connecting to the Go over ethernet, are you on the same subnet as the Go? If you are and it is still not working, try the ‘Manual Connect’ method detailed below.
In the Moku Desktop App, click the settings gear in the bottom-right of the screen, select Connect, then Manual connection…
Then just enter the IP address of the Moku:Go which can be copied from the device select screen.
Please let me know if you are still not able to connect using ethernet this way. If you are able, also try connecting to your Moku:Go using the WiFi hotspot and see if MATLAB is able to connect through this method.