[Cause]
The communications on the DeviceNet network are too heavy for circuit boards to communicate with the equipment. Or all other nodes have been disconnected from the network.
[Countermeasure]
Check that the board and device baud rates are the same. If the baud rates are correct, turn off power to both the controller and the DeviceNet network, then turn both on again. Also check device connections to the network to avoid disconnecting all other nodes.