Hi BetterRed, I've had CAlibre for years, and like you have done loads of updates without any issues whatever - it's only this last upload that's made the Libraries disappear. I my defence I have no idea who the respondents are or what their skill sets are ( you say they are mods and developers but where do I see that?). Don't get me wrong - I'm thankful for their help and advice, but like I say, when you're at risk of losing 22,000 books if it goes wrong - you want to be VERY certain before you take any action.
Whilst YOU know what the advice means because of your intimate knowledge of the subject, that doesn't mean it's as clear to others.
I have now nervously tried the "switch/create - use existing" advice and I'm pleased to say I have now recovered some libraries. So thanks to those involved.
P