can't transfer POIs to Magellan RoadMate 860t


I can't transfer a POI from the Magellan POI file editor. Every time I try, the editor says no GPS unit is detected. Yet, the GPS displays "the usb has been connected to the unit", Windows device manager shows that a Magellan RoadMate is connected by the usb cable and is working successfully. I am running Windows XP, service pack 3. Is there another driver I need to load? Any suggestions will be appreciated