This worked for me:
http://forums.adobe.com/message/2977974
I uninstalled ADE.
Restarted computer.
Reinstalled ADE.
Restarted computer.
Factory Reset my Kobo.
Downloaded my library book to ADE.
Then plugged Kobo into my laptop.
ADE automatically detected Kobo and reauthorized.
Synced to Kobo.
Book opened perfectly!