Hi,
CAN4 Adress is used in CombiStar3000 device (you didnt tell us which device you have, or at least serial number of press- its always usefull to help you out if i could have this basic infos from you) for conductance measurement in fresh water inlet before Dampening solution dispenser.
Check CAN address in the device control.
Check connection or damage on Electrical supply cable.
Check power supply.
Acknowledge fault.