@KateKrueger, this problem has been there for a long time, sadly, and it is related to the warehouse. As long as it's being received into a different warehouse it is apparently OK, and I can think of absolutely no business reason that this should be allowed. This caused us great consternation with the Service Center product. At one point I wrote an override for adjustments to disallow it, but I haven't had that code in a long time. I believe that DSD has an enhancement that forces a serial number to be unique for a given item across warehouses.