Everything was up to date, and my device was recognised--it had to have been one of the books. I'm adding them in batches now--so far so good. I haven't hit the "problem child" yet, but now I know what to look for.
I've also noticed that now my Kobo Desktop is also recognising the books, and updating my "last added" books accordingly.
What a relief. And thank you all again--this is a great forum and resource.
