Try changing Settings/System Settings/USB Mode to MTP and see if that works.Then try MSC. Don’t use Auto.
But it depends on how you put the music on the Fuze.
WMP goes via MTP mode. A computer (or Xbox) can only see music transferred in one mode at a time: MSC (works like a flash drive) or MTP (controlled by Windows Media Player). The Fuze itself sees everything, regardless of mode.
Xbox is supposed to work with MTP. So if you transferred files by drag-and-drop, through MSC, Xbox may not see them.
But you need to experiment. Try transferring files in both modes, Try moving a file onto the root directory of the Fuze (just the driveletter, like E:\Sansa Fuze) and see if the Xbox sees it.