kobo ereader says book isn't authorized

I have a kobo h20 ed1. 

Trying to get a book from the public library onto the ereader. I can read it off my computer, but it says it isn't authorized on her kobo ereader.

I've deauthorized the computer and reauthorized it. It says the ereader is authorized, so why can I not read the book on the ereader?