hgmnetwork haciendo este cambio funciona
function runPostCreateUser($smarty, $username, $id_user)
{
;
// $r = $this->_pACL->setUserExtension($username,
// (trim($_POST['extension']) == '') ? NULL : trim($_POST['extension']));
$r = $this->_pACL->setUserExtension($username,implode(';',$_POST['extension']));
if (!$r) {
$smarty->assign(array(
'mb_title' => 'ERROR',
'mb_message'=> $this->_pACL->errMsg,
));
return FALSE;
}
return TRUE;
}