Carrier BACnet Interface

I am trying to connect a Reliable Controls system via BACnet to a new Carrier 35ton VAV unit. The BACnet interface is an Universal Protocol Interface supplied by Carrier, ( Built by Automated Logic ) and converts CCN to BACnet protocols. The setting for Baud Rate, Protocol setting Modbus/Bacnet/N2 and address setting are all correct but the device does not appear to communicate. We had this issue back in 2011 with Carrier equipment and had to switch to an older version of Carrier's BACnet interface to get it to work. The older unit is no longer available. Has any one else had this issue? Carrier tech support was no help on this issue.