Could you please create a new catalog at a different location and import the corrupted catalog in to the new one by following the below article:
I'm working on it! But first attempt it stopped half way through with an error message "Lightroom is unable to import this catalogue due to an unknown error" or words to that effect. I'm now trying again by importing only groups of photos, in the hope that I isolate the problem (two thirds of the catalogue has so far imported successfully in this way, but I'm now hitting a problem again) Presumably the hope is that once I have imported the whole catalogue (possibly excluding the problem area, whatever that turns out to be), that should be "clean" and so can become my main catalogue. I may not be able to finish this evening (or even for a day or so) because of other commitments, but will report back once it's sorted (I hope) or not.
Thank you for the suggestion.
I've got there - thank you
What I found by a process of elimination by importing folders from the corrupt catalogue in ever smaller groups was that there were two folders that didn't want to import into my new catalogue. No obvious reasons - the photos in those folders seem absolutely fine when viewed outside Lightroom. Anyway, I reimported the photos in the relevant folders direct from their location on my hard disk and that worked (I lost some of the edit trail, but my workflow involves saving as a high quality jpeg once done, so I have a final edited copy) and all seems to be working in the new catalogue.
Not something I would want to repeat (a seemingly totally corrupt catalogue, which I initially thought I had, was a heart stopping moment, and the eventual rescue process proved tedious because of the need to do it in stages, many of which failed until I had homed in on and excluded the two corrupt folders), but at least it' was resolved.
So thank you
There is still the mystery as to why the original catalogue corrupted so completely but hopefully that's a one off!
Thanks for the update.
Good to know that everything is working in the new catalog.
And yes Catalog can get corrupted because of ones workflow or communication of Lightroom and the system.
At the moment catalog backup would be helpful rather than creating a new catalog sometimes.