I've done that. Thank you. My collections are now back. I've reverted to Manual Management for now but I may use the automatic one. It seems to work very well and would save me time in the long run. I have thousands of books to add to my library yet. It's a slow process, because I'm picky about how they are organised (I used to be an Archivist

), but version 7 has made that process much more efficient. This was my only issue so far (fingers crossed).
I have no idea why it happened, but I'm sure you'll figure it out
Thanks again