Meaning: The minimum duct thickness value for the cross section size was not found in the Minimum Duct Thickness Rule. The size might have been deleted from the catalog after the duct was placed, or the duct was resized and the new duct size does not have a corresponding value in the catalog.
Recovery: Contact your catalog administrator. Have them add the minimum duct thickness information for the cross-section size to the catalog. Alternatively, you can resize the duct to a cross-section size that has and entry in the rule.