Windows forms navigate webrowser method not available?

Question

I try to navigate to a url and send a new http header with phalanger but when I use the navigate method it gives me an error message there is no method available (even with overload and so). How can I send my own http header? Example:

This dosesn't work: this->browser->Navigate(new \System\Uri($url),"_self",null, $authHeader);

This works (but it navigates only to the website w/o sending my header:

this->browser->Navigate(new \System\Uri($url),$authHeader);

Edit: This works, too, and is the more correct approach but I want the thing with the additional header!!!

this->browser->Navigate(new \System\Uri($url));