{
global $Ajax, $SysPrefs;
- if ((!isset($SysPrefs->no_check_edit_conflicts) || $SysPrefs->no_check_edit_conflicts==0) && get_post('cart_id') && $cart_id != $_SESSION[$cartname]->cart_id) {
+ if ((!isset($SysPrefs->no_check_edit_conflicts) || $SysPrefs->no_check_edit_conflicts==0) && $cart_id && isset($_SESSION[$cartname]) && $cart_id != $_SESSION[$cartname]->cart_id) {
display_error(_('This edit session has been abandoned by opening sales document in another browser tab. You cannot edit more than one sales document at once.'));
$Ajax->activate('_page_body');
display_footer_exit();