single vote in same ip network

Hi there,

maybe it has been asked before but I don't find the answer.

I have place the:
<?php
// Important! You have to include it before your html code
include_once "poll_cookie.php";
?>

on top of my page. And I am using the "do not verify" option.

I want that my students that has the same ip at school can vote only once with the cookie veirfication...

but it is not working...

any ideas...

check it www.robo-tic.qc.ca/sondage/fr.php

thanks