Actually, it's not an error. There is no form with the requested fields. Is the url correct? Any syntax problems? Try this: 
#!/usr/bin/perl

use strict;
use warnings;
use WWW::Mechanize;

my $url = 'http://www.example.com/cgi-bin/testcode.tcl';

my $mech = WWW::Mechanize->new( autocheck => 1 );
$mech->get($url);

my(%fields) = (
    modem     => '1122.3344.5566',
    ip_select => '1.2.3.4',
);

my $result = $mech->submit_form(
    with_fields => %fields,
);
print $result;

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In reply to Re^3: Submitting a second form by Khen1950fx
in thread Submitting a second form by rp132

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