The message is telling you that, when you downloaded those ebooks, you were
using a different user ID for Digital Editions. Somewhere you changed it,
and since Digital Editions keeps track of such things, it won't let you
read ebooks under that 'old' ID. If you can backtrack and find out what
that old ID was, you can re-set Digital Editions to the old ID and then
you'll be able to read those ebooks. We can tell you how to do that if you
find that old ID. If you've downloaded ebooks under the new ID, you'll
have to change Digital Editions back and forth to be able to read them.
This happens fairly often. It's usually because of a re-install of Digital
Editions or changing something on your laptop that required you to
reinstall your OS.