I can't delete Some files

I've had this happen too--you gotta be in MTP mode to really take advantage of the true ease-of-use of this little gem. The solution here is to physically delete the file from the player on your desktop. If you can't delete the file there then you might have to reset the factory settings (eek).

Also, if an mp3 track doesn't have a title (or a filename), it will show up as "Unknown" on the player and it will not play. You have to physically give the file a name by dragging it to your PC desktop, naming it ("properties") and then copying it back. It forces you to keep a clean music library for sure!

FYI: Trying to do stuff in MTC mode I've found to be a real pain (and, no, you DON'T have to be use MediaPlayer to transfer mp3 songs, albums, and playlists--drag-and-drop works in both modes). Use MTP mode for the real experience.