[marketpress] Problem adding items to cart in MultiSite setup

I have purchased, downloaded, installed MarketPress on our multisite setup.

It is currently set to Enable Global Cart.

I ran into problem when adding an item to the global cart, from the main site.

This is the link to the main site store, which has three products (it displays 6 because there is another 3 from child site).


The second sample site belong to the network:


So if I go to main site, add a product, then try to check out, nothing is in there.

However, when I go to the child site, add a product, and it does go to cart.

Could some body please help. I’ve got really stuck.