I have lightroom 5.7 currently. I cannot get it to open this morning. I get the following dialogue box. Lightroom encountered an error when reading form its preview cache and needs to quit. It says it will attempt to fix on reloading. I have restarted the computer and still get the message. Any help would be appreciated.
Open the folder that contains your catalog and look for a folder with the extension .lrdata. That is the previews file and it needs to be deleted. Then Lightroom will create a new one.