Support

We will need you to paste us the Target URL as well. From the looks of it, the user session expires (which means that the administrator is logged out) but the user interface of a back-end component (most likely Virtuemart) which is still open in the browser is trying to perform an AJAX request without checking what it gets in return. Normally, components using AJAX requests are supposed to check the return values to prevent making subsequent requests to the back-end if the user session has expired. But since we are talking about Virtuemart and its extremely questionable development practices I think it's VERY likely that it doesn't check anything at all, causing this issue. In this case the only thing you can do is disable the administrator URL query parameter protection in Admin Tools, knowing that you are degrading your site's security to cater for a badly written component.