Probably a version incompatibility. Try rename file /html/com_virtuemart/cart to /html/com_virtuemart/_cart to disable the override and use original file from VM.
I have never received an access from You. Please send it so I'll be able to make some tests and fix the problem. Also make a backup of Your site and update joomla to the latest version. I'm not sure if newest VM doesn't need it.
Yes. I've just dug through my PM's and found message from You, but unfortunately the access to folder is not working. Please send it one more time to my mail directly, to speed it up. You can find it in the footer of my every post.