This message is telling you that the MNGP "Display" is not able to communicate with the Classic. The most common cause of this would be that the address the MNGP is looking at got changed to one that is not on the network. When at the Home screen or main status screen there will be a word in the middle at the top. On a single Classic this should say Classic if it does not say this then you need to use the up and down arrows to find Classic. The MNGP should regain communications when this is set correctly.