Sync (and drag/drop) only allows for one song at a time

So this is the second SanDisk mp3 that I have got in the past month, the first had a frozen screen, and now the sync is not working.

When using WM Player 11, the sync list only transfers one song and then stops. I'm having a similiar problem when I drag/drop songs onto the device. The transfer file status box will go to a 100% and then stay open. The file transfers, but it's a royal pain putting one song at a time.

please help!