Hi

I have just installed he builder, created a fresh page, and added a widget. When I try and preview the page I get 

An error has occurred while processing your request.

You may not be able to visit this page because of:

• an out-of-date bookmark/favourite
• a mistyped address
• a search engine that has an out-of-date listing for this site
• you have no access to this page

This happens no matter what I add onto the page.

Joomla 3.9.21

Please help

thanks