Small tutorial for export & import data from/to Mapsource for "USB mode" compatible devices.

Make your project in Mapsource. Contents of project what be imported depend of compatibility ypur device. Nuvi import only waypoint usual. Some model of Nuvis import routes. And moto, tourist and portable sometimes import tracks.
Save project for assurance in Mapsource format. Then save file - do "Save as..." - choose "Save as type" - find "GPS eXchange format" *.gpx - destination on your PC.
Farther connect Nuvi. Copy your project.gpx to folder GPX on Nuvi root. Do not replace current.gpx and so do not give name like this for your files. current.gpx is device service file and device do not any chance for control by it. After rebooting your device you have all contents in your device. If successful you can see your data on screen and in current.gpx cos current.gpx is mirror of stored in device data.
P.S. Nuvi 2xx and other old devices delete your file automatical from Nuvi. New device keep your project file in folder. In this case if you delete waypoint from device by menu the device restore your project contents after reset only. Do not want to this restore - delete project.gpx after rebooting.

For export to PC you must open current.gpx in Mapsource simply.