Sorry, I mistakenly deleted your posts.
Ok, so as you have uninstalled virtuemart, but have AwoCoupon pointing to Virtuemart, the error occurs. Can you try going to this link:
If you can get in, you should be able to change the shopping cart. If not, then it can be done through the database. The other option is just to uninstall and reinstall AwoCpouponm, this would delete any virtuemart coupons you have in the system, but since you are swithing carts anyway, this should not be a problem.