Hi - it's just a php warning - you shouldn't show these for a production site but this can be set by your host.
To not show it you can add this line
error_reporting(E_ERROR);
to the top of public_html/SITEWEB/leonard/templates/leonard/html/com_virtuemart/cart/select_shipment.php
[code type=php-brief]
// Check to ensure this file is included in Joomla!
defined('_JEXEC') or die('Restricted access');
error_reporting(E_ERROR);
include_once dirname(__FILE__) . '/../assets/includes/flexibleMartGlobal.php';
[/code]
cheers