hi,
After renaming the "user" and "cart" folder with in /templates/html/com_virtuemart/, you have completely eliminated the CleanMart from shopping cart page. Your shopping cart page is now using official Virtuemart layouts.
If the OPG still doesn't work, then this failure can't be related to CleanMart. Try contacting to the developer of the OPG plugin, because this is their extension and they are the ones who might know what goes wrong.
Regards.