That error just means the Server Behaviors panel hasn't been opened. It happens with the latest version of Dreamweaver. Just open the Server Behaviors window before editing the cart and that shouldn't happen.
In terms of the two shipping charges you could probably add a column to the cart for "ShipFlat" and then set it to 0 or 1 based on the shipping. Then you can have to shipping calculations based on that value to calculate the correct total.