MarketPress is not adding products to shopping cart

This is on a multisite install, it was working fine, now it stopped adding items to the cart. I tried on another dummy site on the same network and it worked fine. The site is http://delisuss.com/menu and the cart is on http://delisuss.com/menu/carrito

This is time sensitive since it was working and we were about to launch the site, but it stopped working.

The only modifications I have made to the plugin were to the language files to "improve" some of the spanish translation and to finish localizing some aspects that weren't localized. Other than that I have made no changes to the plugin. I have also re-installed it fresh from scratch overwriting my language files and that made no difference. I also deleted the DB entries for mp_ and then totally fresh installed again and it still is not adding products to the cart.

I have some JS running on the site and I also disabled that and still no luck.

Any help would be appreciated and I would gladly pay for someone to take a look at it if it is beyond the abilities of the support forum to fix.

Thanks Much!