Starting LR 5.7/Win, get a message LR has encountered a problem with Previews cache and needs to quit, will to fix on restart. But after many restarts nothing changes
There are lots of threads on this issue which crops up regularly. No one has come up with a reason why. The Previews files are corrupt
The simple cure is to delete the Previews files and then have Lightroom rebuild the Previews.
See to the right side of your post for help under "More Like This"
Thanks for your help, will give this a try.