Thank you so much for your reply, Mike. It helps to understand that this was created by, once again, an Ebay change. But anyone who depends on this feature really needs it back immediately, so whatever the technicians can do to speed up the fix would be greatly appreciated. Please stay in touch about it if you can.
By the way, Sadie, I would suggest a much easier work-around than the Auctiva rep suggested initially.
Here's what I'd do: via Auctiva, just create your listing normally in every respect except adding the product from the Ebay catalog. Go ahead and launch the listing via Auctiva as normal. Then go into your Ebay account to revise the listing, and simply add the book to it. It's much, much simpler and quicker in my opinion.