10400 - Transaction refused because of an invalid argument.

When trying to process a payment I received this error:

There was a problem connecting to PayPal to setup your purchase. Please try again.
10400 - Transaction refused because of an invalid argument. See additional error messages for details. - Order total is missing.

Fresh install of wordpress & marketpress, one shop setup with 2 products - can be found here:

http://www.artzy.co/bradydyer/store/products/