I tried many things, but what worked in the end was a suggestion from a thread last year. I opened my KOBO and signed off. Then signed back in. That seems to have done the trick. I can now download library books to ADE then transfer to the KOBO and actually open them. HURRAH!! I mainly use my KOBO to read library books and was panicing about losing access.
Before that fix I reauthorized my computer and my KOBO.