WPBakery upgrade

I have updated my site with WPBakery 6.8.0 and activated the Plug-in.
I create new Page, paste in some text in Backend Editor and then published the page. My problem is when I click on Frontend Editor a pop-up appears saying ‘Sign in to access this site’. Username & Password entries are required for authorisation by https://www
I don’t know where to turn for help to debug my problem.