Can anyone give me a clue?

I have a Sansa Fuze 8 gb and I use it for audiobooks almost exclusively.  When I'm trying to remove some of the books I've already read, I get the following:

                                Cannot delete (Title): The storage is write protected.

                                 Remove the write-protection and try again.

      I would like to know how to remove said "write-protection".  I haven't had any luck with the manual or any of the sites I've searched.

Thanks.

             the bookworm