Old delivery was picked and packed, but the users for some reason decided to reverse it. While doing that they probably reversed the picking and then deleted immediately the delivery without deleting the handling unit assignment first. Then they created a new delivery for the same sales order and try to pick the sales order specific stock which is packed in this handling unit. Actually the transfer order will run into an error, because the specific stock is packed in a handling unit which is still assigned to the old deleted delivery (VEKP-VPOBJKEY).
We followed few steps to remove assignment of HU. but that field is now grayed out. we can not use it now. (i have attached screen shot of error message)