Hi,
Did you touch this PHP file?:
/modules/mod_flexible_cart/tpl/default.php
or this:
/plugins/system/vm2_cart/vm2_cart.php
If you touch either of those PHP files, you probably broke the AJAX scheme.
To retrieve your changes back to stock, re-install the "Flexible Shopping Cart Module” (re-install both the plugin and the module)
If you want to make some customizations. Don’t touch the DIV class names, don’t change any DIV or SPAN element (inside the PHP files).
Do your customization only through CSS. Don’t touch the PHP files of Flexible Dropdown Shopping Cart Module or Plugin PHP files.
Regards.