If you receive this error message when shipping an order with Endicia/USPS, that means that Endicia is communicating an issue with the customs information currently in the Order Window>Customs tab. Check the following before trying to ship the order again.
Ensure that all products in the customs tab have a weight input that is more than 0.
Make sure that the total package weight is equal to or more than the sum of the product weights listed in the Customs tab.
Check that the value of the products reflects the actual value of the order items, even if you are not charging the customer for them.