When I try to launch Lightroom I get this massege: "Lightroom encountered an error when reading from its preview cache and needs to quit. Lightroon will attempt tp fix this problem the next time it launches." but when I try to launch it again, I keep getting the same messege. How can I solve it?
With Windows Explorer or Mac Finder, go to the folder that contains your LR catalog, typically inside Pictures or My Pictures.
There will be a folder, named [your catalog name] Previews,lrdata
Delete this folder - do not delete anything else.
Lightroom should now start normally, and will rebuild the previews.