Silly Authentication required popup when doing logout in cookieless session HTTPS server

On http, locally, everything works fine: pressing logout (it's loginstatus control) redirects a user to login page. But when publishing site on https server - i get 'Authentication required' popup (?) If i press cancel there - i finally is taken to Login page, but this is annoying! Why it happens and how to avoid this?? My logout method is following: protected void loginStatus_LoggedOut(object sender, EventArgs e) { HttpContext.Current.Session.Abandon(); FormsAuthentication.SignOut(); FormsAuthentication.RedirectToLoginPage(); } ...