I'm glad to hear that you got past the error regarding the built in shipping rule. In the screen shot for your new charge rule in the calculation portion it looks like you are basing the shipping on a particular items quantity.
If you would like to apply a flat rate shipping charge you would just select 'flat rate' from the dropdown and enter the amount. If you wanted it to be based on the total number of items in the cart you can choose 'based on a column subtotal' and select the quantity or any other column that you would like to base the shipping on.
Please post back and let us know how it works for you or if you have any further questions.