Permalink structure for market place / cart link error

is there some special permalink structure I need to allow marketplace to function correctly?

I have installed marketplace plugin on a site that is using domain mapping

I have added a custom menu with a hard link to the cart (mydomain.com/store/shopping-cart/)

I can add things to the cart no problem

but the link in my nav ends up at mydomain.com/cart and I get a 404 error

also the link for the store page to the cart does not work

you can see it here http://www.hcgweight.net & http://www.hcgdrops.net

have not tested to see if having an item in the cart makes a difference

the only way I can get to the cart is via the buy now button