Error after HU packing in Outbound Delivery

Hello All,

I unpack existing Handling Unit (HU) in an outbound delivery in VL02n transaction and pack part of its quantity in new HU that I create on same screen. Now, while saving this delivery I get this error "Movement type 990 does not allow immediate confirmation". Even when I delete existing HU nd pack all its content in new one I get the same message while saving the delivery.

Surprisingly for the same packing material and packed material in another outbound delivery I can do this operation without any error message.

What can be the possible reason for this. Please help me out.

Thanks,

Amit G