Page not found error 500

Can you please reinstall JEvents? It looks as if the calendar layout has been removed of the site.

the calendar layout work perfect https://www.maremmainfesta.it/ricerca-eventi/calendariomensile/2017/8.html

Ok I see now. Where did you get the URL you showed in your first message? That URL comes with no menu item, so JEvents, when trying to get the correct URL to the page uses the default menu item which seems it's not JEvents related.

The fix for this is to avoid the url you showed in your first message.

the error show in google search console

You need to find out why is Google getting to your pages without menu item. Maybe you have a manual link somewhere in your page.

is possible hide the search bar?