Why does my borrowed library book not appear on my Nook?

I use Adobe Digital Editions 4.5 to borrow books from my library to read on my Nook.  I just borrowed 2 books from the library.  I transferred one to the Nook without a problem.  I used the same procedure to transfer the second book but it does not appear on the Nook.  If I open My Files on my laptop while the Nook is connected and view the Nook's files, that second book is listed.  And if I go back to ADE and try to transfer it again, I get a message that there is already a file with the same name in the location and I am asked if I want to copy and replace it.  So it appears as though the book is in the Nook but I can't find it.  It is not in the Nook's library.  The first book I transferred, by the way, is in the Nook's library.  Can anyone tell me why this is?  This problem has been going on for months.  Barnes and Noble is unable to help.