Occasionally I have an issue where I can't communicate with a Panelview 800 over Ethernet.

I can ping it and see other devices on the network. What I have found is you have to reset the Panelview to out of the box condition by plugging a keyboard into the back of the Panelview and holding the CONTROL and SHIFT keys at the same time. Note that this will clear all the data out of the Panelview.