Nictitate authentification problem

hello,

I search in vain for a solution to a problem message: “The server (mine) is ask asking for your user name and papssword. The server reports That it is protected from administration. “
This problem is Nictitate-free theme, as it does with some other issues and I have not had to change host side.
This authentication request is made at each login pages and articles on the site except the “portfolios”.
This authentication request is present on all devices (mobile, computer) and all internet browsers.

Do you have an idea of the problem? The problem would come it a php file, if so which and how much?

Waiting for your return and thank you.