ADE no longer recognizes checkout of a library book that I was reading on it only 2 days ago. "No record for this loan was found on this machine." It doesn't say where it looked or what it would look like. I'm stuck!

Prior to this issue, I was trying to figure out how to download books from ADE to my Sony reader, which it had refused to do.  That left me reading my library book only on my computer, unsatisfying.  This morning I tried something new.  With my Sony reader already connected to my PC, I started ADE.  That's when ADE first told me "No record for this loan..." as written out above.  But when I had ADE open and with the reader icon showing in ADE, I de-authorized my computer and re-authorized my computer.  Now I can transfer a book I already owned from ADE to my reader, but it still insists that I can't do anything with the library book because no record for this loan was found on my machine.  I did a fresh download of the book, and I downloaded another library book and it also refused to open either of them, even though the latter was checked out after my re-authorization of the computer.  There's very little that makes sense about this.  I would appreciate some help.