i've resolved the problem, it's DOM problem with IE thought, infact
the function MLD.set_waiting_message(div); puts a loading gif into the
div where there is the form, so when i submit with form.send() IE
doesn't find the Element form, to solve i've putted the function after
form.send()
onValidateSuccess : function()
{
var div = $('request_div');
var form = $('request_form');
form.removeEvents();
form.set('send',{
update:
'request_div',
onComplete:
function(response){div.set('html', response);}
});
form.send();
MLD.set_waiting_message(div);
}