I have a purchase order for 10, the supplier ships 8 there are 2 on order, the supplier tells me they will never ship them. The 2 shipment need do the reversal by set the negative quantity in receive quantity field.
in AX2012 is not allowed to do that. and i believe there is another way to post negative quantity.
you have PO for 10 Qty and received 8 Qty and you made Product |Receipt not simple cancel the remaining qty and your status of open order will change to receive and then you can proceed for the invoice.
in some case the order status will show you received and you will get the problem and if you check the on hand stock for this item it will show you 8 instead of 10 so in that case you can open the PO and select that item under update line there is delivery reminder option click that and cancel the qty this will also change your status from open order to received.
If you order 10 and receive 8 you will have received 8 and 2 will be on order - using the deliver remainder function will cancel the 2 - you should not enter -2 because then you will have received 6. I would also suggest you are entering a negative quantity and value which maybe giving you your issue, make the unit price positive. Or post a screen shot of your line entry.