When attempting to import a layer into Post Configurator... the user is alerted that the import layer with the same order as an existing layer is not allowed. (Please see image below.)
Please see attached video for detailed explanation.
Note: The layer that is being imported must have the "Order" parameter changed in the .psl file. Both ".psl" files contained an order <Order>9000</Order> . Simply change the Order number in the layer to be imported, to a layer number that does not currently exist in the layer with the duplicate Order number.