I have a Kobo reader with the same problem. I can download books from the public library, and just bought two books from Kobo. I can read them on my computer, but can't open them on my reader; I get the same "OOPS" message. I've authorized my computer and the reader and under "Authorization Information", both devices have the same Adobe User ID number. The eReader is new but there's something about it that Adobe doesn't like.
I've had these tussles with Adobe, and there's something about Adobe that I don't like.
Addendum: My Kobo reader gave up the ghost completely. Still under warranty, I received a replacement unit and, guess what--this problem with opening downloaded books is gone! I can read books that I've recently purchased, plus a library book that I downloaded an hour ago.
Beats me why--if another problem surfaces I'll tap an add-on to this add-on.