That sounds odd. Usually if it's a bad download it only affects a book or two, not everything. Have you tried archiving-synching-unarchiving, yet? If that doesn't work, try shutting the NT down and then restarting. You could also try a soft reset or a even erasing-deregistering. Are these all ebooks that you downloaded through B&N? If not, where did you sideload them from and what format are they in? Also, what firmware version are you running?