Search form doesn’t work

Hello there, in the link provided the search form in home page doesn’t work.
I tried to create another list + cat + attribute but there’s no way that the form works.
I don’t think it is a theme problem, ’cause i tried to put it in via widget and shortcode.
If I simply click on search without filtering, it pops out a “Forbidden
You don’t have permission to access this resource.”

Anyway, any list page works well, as you can see in the menu.
Any clue?

Thanks!

E.

The page I need help with: [log in to see the link]