This cant be so complicated. Unfortunately it can! Adobe has taken something that was really important to make easy for even people completely unused to computers, and made it into something that is a nighmare even for computer experts.
Just checking,
- The problem is with a book newly downloaded from the library?
Just to make sure, now things are in what ought to be a working state can you borrow and download another book
and see if you can get that to the Kobo and read it.
If you downloaded the other book while you were in some sort of in-between state it could be that the other book is authorized in an odd way. - You can read the books on ADE itself, and download them to the Kobo?
The only thing that doesn't work is trying to read them on the Kobo once copied?