my $mech = WWW::Mechanize->new( agent =>$browser_agent);
$mech->cookie_jar(HTTP::Cookies->new());


$mech->get($url_login);
$mech->form_number($form_nummer);
$mech->field('username' => $username);
$mech->field('password' => $password);

$mech->click();  <--- I think this is where the error gets trown, if the "username" textbox is not present