Non-shippable product cancels Flexicharge shipping amount.

I am having a problem with Flexicharge shipping where I have some products (Publications, T-shirts) that are shippable and others (Membership, Events) which are non-shippable. The charge works fine with the shippable items alone. My problem arises when I try to add a non-shippable item into the order; the charge is completely canceled out.

You can check it out at: http://www.vtarchaeology.org/cms (you will have to create a user account however to access the checkout)

I need to launch this site ASAP so, if anyone has any insight into this issue your help would be greatly appreciated.

Thanks.