Sony is totally unhelpful. Adobe is totally unhelpful. But MobileRead forums are VERY helpful! After toomanybooks suggestion, I installed the Sony Reader Library software, even though it doesn't work on my machine. But when I did it DID install the appropriate drivers, and then ADE could find my ebook, and I'm reading again.
So thanks all. And yes, you do have to have some Sony drivers to make it work it appears.