Trata de utilizar siempre DOM2
Código HTML:
<script type="text/javascript">
function post_form( id_form )
{
document.getElementById(id_form).submit();
}
</script>
<form action="index.php?modulo=verficomision" method="post" id="verif1" name="verif1">
<input type="checkbox" onClick="post_form('verif1');">
</form>