Can you post a copy of the manual, I'm sure it makes sense for someone at the forum.Just got the NAV+4 and was looking for any help on using the USB interface. The manual that comes with it is no help at all!
I connected a USB thumb drive with some MP3 files on it to test, but all I get is a please wait message on the display.
What kind of a thumb drive was it, how much data and how was it formatted? Are you sure the music titles were MP3-coded?
I'd suggest trying first with a few titles only, proper format etc.