Ext not defined VirtueMart
To solve this problem we need to disable the usefetchscript function that VirtueMart uses
Open the /administrator/components/com_virtuemart/virtuemart.cfg.php file and add the following line
$_REQUEST['usefetchscript'] = "0";
above the line
and save your changes.
Refresh the VirtueMart Administration Panel and the problem will be solved.