Having trouble with book rented from library

I recently rented a book from my local library and downloaded it to Adobe Digital Editions 4.0.  When I went to copy it, I was given the error message "Copy Not Allowed".  I researched this and found that I needed to authorize the computer with an Adobe account rather than without one, so I changed the authorization to reflect this.  I still could not copy the book.  Frustrated, I decided to return the book to the library and try again another day.  However, when I attempted to return the borrowed book, I was given the error message that my computer was not authorized - which I then double checked and it is.  Can someone help me get this book out of my library and back to where I rented it from?