We noticed that all of our items were using average costing method and were changing to lot-numbered for lot-numbered inventory and specific for serialized assemblies. But now that we try to make work orders, we get the error "FIFO and LIFO cost items may not be used on a work in process work order". I saw another post that confirms this but I need more details. Like why is this? We are in an industry where the same item can have cost variability and we want to be able to apply that variability to specific jobs.