Ok, I discovered what caused my problem, but I dunno weather this is a bug or a feature?

When I plugin my ZEN device a icon of the device appears on the desktop. Starting Gnomad gives me the error: "no jukeboxes found on the usb bus".
If I now unmount the device, but keep it plugged in, and then start Gnomad then everything works perfectly!

Perhaps this is something to notice in the manual? Or is it there already?