G-3 modem connection as serial port

I have my Media 100 version 5.5 installed in a desktop G-3 (Mac OS 9.2). A videotape machine(Panasonic AG-DV2500) is hooked up via a remote cable to the modem port. When I go to the hardware settings to turn the remote control settings (DQ-Timecoder) there is a DiaQuest screen that appears(version 2.2M) that says "Video Deck Connected to". The next line is blank. When I hit OK a box comes on that says "The Diaquest device control plug-in cannot use the port because it is in use by Appletalk or another application" Hit OK and another box appears that says "Unable to switch to selected machine control method".
I have exhausted all the extension folder and Appletalk activation and deactivation options that I am aware of to no avail. The deck and cable are good because they were tested on another system. Any suggestions? How can I turn on the serial capabilities of this port? thanks.