Hi,
Solutions are so easy to handle.
1- Open this PHP file:
plugins/system/flexibleTemplate/flexibleTemplate.php
and to the 69th line, include this line (copy-paste from below):
2- Open these PHP files:
/templates/TEMPLATENAME/html/com_virtuemart/cart/default.php
/templates/TEMPLATENAME/html/com_virtuemart/cart/default_address.php
in both of those files; to the top (after <?php), include this line (copy-paste from below):
you won't see any "undefined variable" error message no more, because you are defining them (as blank variable).
Regards.