A CAN Bus network must have a terminating resistor between CAN High and CAN Low for it to work correctly. For maximum range over long distances, the ideal termination is one 120 Ohm resistor at each end of the bus, but this is not critical over short distances.
Each VBOX has a resistor built in to terminate the CAN Bus shared with other Racelogic modules. If however, Racelogic modules are used without a VBOX in a 'standalone' mode, it is important to check that the CAN Bus has a termination resistor fitted. If in doubt, measure the resistance between CAN High and CAN Low without the system powered up. The resistance should ideally be less than 120 Ohms and closer to 60 Ohms if a resistor is fitted at each end of the bus.
CAN bus systems which are already active (i.e. a vehicle CAN bus system) will already have the correct amount of termination.