WWW::Mechanize problems

Hello,

I have a problem with WWW::Mechanize that I cant solve. I am posting to 
a site but apparently I get always to the same original site.

my $mech = WWW::Mechanize->new(stack_depth => 1);
...
my $url = URI->new("http://rna.tbi.univie.ac.at/cgi-bin/RNAfold.cgi");
...
$mech->get($url);
...
if($mech->success())
            {
                $mech->form_number(1);
                $mech->set_fields(
                            name        => "$names[$num]",
                            Sequence    => "$lines[$num]",
                            pffold        => "pf",
                            Params        => "RNA",
                            Temp        => "37",
                            email        => '[email protected]'
                         );
                $mech->untick(toggles => "-4");
                $mech->untick(toggles => "-d");
                $mech->tick(toggles => "-noCloseGU");
                $mech->tick(toggles => "-noLP");
                $mech->untick(plot => "on");
                $mech->untick(SVG => "on");
                $mech->untick(SSview => "on");
                $mech->click_button(value => "Fold it");
                if($mech->success())
                {... do something

I never get to the next page. Arrays @nams and @lines are not empty. I 
checked it with submit with some hardcoding for Sequence but there is no 
chance to get past the original site. Do I anything wrong? I am lost I 
am afraid. Thank you in advance for any advice.

Sebastian