IdHttp Authentication does not function

Hi, I have written a simple program for download and view a web page with IdHttp Indy component (Indy version 9). The problem occur when i try to download a page that is in a directory that requires authentication. With Internet Explorer I can easy make this by filling the classic prompt window with my username and password. With Indy I use this code:

procedure DownloadPage;
var
  lStream: TFileStream;
  sWebPage : string;
begin
  sWebPage := Edit1.Text;
  lStream:=TFileStream.Create(ExtractFilePath(Application.ExeName) + 'page.html', fmCreate or fmShareDenyNone);
  try
    IdHTTP1.Request.BasicAuthentication := True;
    IdHTTP1.Request.Username := 'myusername';
    IdHTTP1.Request.Password :=  'mypassword';
    idHTTP1.Get(sWebPage, lStream);
    IdHTTP1.Disconnect;
  except on e:exception do
    showmessage(e.Message);
  end;
 lStream.Free;
end;

On get method I receive the error: HTTP/1.1 401 Unauthorized.

Username and password are correct.
There aren't proxies
The procedure works fine with other pages that don't require authentication.

Where is the error ?