Create file htdocs/ajax/grids/users_grid.php
<?php
require_once('../../boot.inc.php');
boot('my_site');
require_once($WSC->get_site_inc_dir().'grids/users/users_grid_ajax_ctrl.class.php');
session_start();
//TODO: to check if it is working
$g_ajax_ctrl = new Users_Grid_Ajax_Ctrl($WSC->get_tpl_dir().'grids/users_grid.tpl');
$context = new Web_Context();
$SITE->run_other($g_ajax_ctrl, $context);