want to write script and put a UDF of duration between PO order date and confirm date

SUGGESTED

error using pre-write

orderdate = ""
confirmdate = ""


retVal = oBusObj.GetValue("PurchaseOrderDate$", orderdate)
retVal = oBusObj.GetValue("UDF_PO_CONFIRMDATE$", confirmdate)

dateD = DateDiff("d", confirmdate, orderdate)
retVal = oBusObj.SetValue("UDF_CONFIRM_DATE_PASS", dateD)