It is probably erroring on the second line being NULL even though you are entering the quantity on the first line.  Clear the alternates and add them one at at time, or clear the error and enter the quantity on the second line too.

@ronhu The original serialized component 100001 started with QPA = 1 for a Qty Required of 2 for the Lot Size of 2. When you replace (1) of 100001 with (1) of 100001R, the shop order wants to update the QPA of 100001 from 1 to 0.5 (for a Qty Required =1) which is not allowed due to it being a serial part.

You will have to drop the lot size of this order to 1 and create a second order or split this shop order into two orders with Lot Sizes of 1.

@ShawnBerk

@matt.watters

Thank you for your input.

From what you described, we have to make alternate part from the very beginning of the manufacturing in full quantity. partial is not allowed in serial alternate part .

Thank you.

Good call @matt.watters , I missed the first screenshot and only looked at the second one.