I had the same issue with my Sansa Clip as you seemed to be having (i.e. able to browse, but unable to transfer music). I solved my problem by telling Ubunutu to mount my Sansa Clip as "/media/SANSA_
CLIP" instead of "/media/SANSA CLIP" The space in the name was causing Amarok issues when trying to transfer files. I got Ubuntu (gnome) to change the mount point by right clicking on the "SANSA CLIP" icon that was on my desktop, then I selected the "Volume" tab, and then in the "Mount Point:" Field, I entered "SANSA_CLIP"
The tools expect the name of the directory that will be mounted under "/media/" DON"T use any /'s in the name, or you won't be able to mount your clip at all. If you do run into issues, you can fix any mistakes using the gconf-editor