Cancel deliver remainder in Inter-company Purchase Order

There is a inter-company purchase order that have an item to be cancelled in order to change the status from Open order to Invoiced since all the items has been fully invoiced except for the item to be cancelled. I have try to cancelled the deliver remainder in Functions but failed to do so. It is noticed that the item is registered in PO and reserved in SO but On order in Inter-company SO. Therefore, I have tried to unregistered the item in PO. Somehow I can only partially unregistered the item. E.g. I can only unregistered 10 of the 20 items. It stated “10.00 cannot be picked because only 0.00 is/are available from the inventory” when i tried to unregistered another 10.

Is the method done wrong? Or is it cause by system bug as I know there is bug in inter-company cancel deliver remainder.

Please help.

Thank you