Problem with Sansa m240

I have been successfully downloading eaudiobooks from my library web site and transfering them onto my Sansa m240, but today when I tried (several different books), I kept getting the message “cannot create folder.  Portable player does not support this function”.  I tried to have the file put into an existing folder, but received the following message: “unable to transfer the selected title because [insert 3] returned 0x80070070”.  Does anyone have any idea what this might mean?  This is really weird, because I’ve had no problem with transfering up to this point.

what if you use windows media player to transfer the files, does the same thing happen? Are the files .wma?