Every now and then, my client will notify me the site gone with error "Whops, looks like something went wrong" and they cant access the cp with the error "Credential are incorrect" which clearly is correct.

Then I need to go to ftp/cpanel of their hosting company to remove the statche folder (/local/storage/framework/cache/stache). Then everything back to normal.

I couldnt figure out what when wrong with that?

Hosting Provider: Hostgator