Can't get books to "remove" from ADE library??

I am having problems transferring library books from my ADE to Nook.  I was told to remove them from the ADE library and delete the file from the computer.  I have done both, but next time I open ADE the books are back in the library.  I had been prompted when initially removing them to confirm this is what I want and I say yes. Any ideas how to get rid of these once and for all?