Linda--I've been able to successfully load a DRM'ed PDF library book on to my Sony Reader. I used the digital editions software to load the file on my reader. It then shows up when I view books by title. I don't know if it's just this book or not, but it doesn't show up at all when I'm viewing books by author. (It also shows up when sorting by date.)
Maybe the title/author information isn't input correctly for the book you are trying to load. Have you tried another book to see if you can load a different book?