404 error when add to cart

After filling in the custom fields and clicking on Add to Cart, you are directed to a 404 error page. The item was added to the cart, but you are being directed to a missing page. Once I go to the cart, I am unable to remove an item. When I disable the plugin, I can remove items from the cart and am directed to the correct page with no errors. Please help as I am needing to get this site up and going.
http://numoa.com/product/imafs-single-car-registration-numoa-member-entry/

https://wordpress.org/plugins/wc-fields-factory/