[BetterRed]

@thistlebarrow2 - I wonder if you accidentally 'removed' the library from calibre's demesne.

I've done it too many times to count. Its easily fixed:-

1. click the library icon;
2. select Switch/Create library;
3. click the blue button;
4. browse to the library folder;
5. click OK;
6. ensure Use the previously existing library at the new location is selected;
7. click OK.

BR