If you see this message below, here is what to do!
Typically, this error is associated with the Shipping Override Profile being used for that listing. Leaving the field Cost blank will cause this error to occur. If you do not intend to charge for shipping, then you must enter '0.00' for that field.
Once you have correct this and update shipping profile, go back to the listing and click save changes to prompt another sync for that listing. This should resolve the error!