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        => 'some_email@xxxxxxx'
                        );
               $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