When changing the quantity on a ship doc you may receive the error.
"Cannot edit the quantity directly because a sub form has more than one entry"
This message means that you have lot or serial # or multiple bins allocated thru the bin or ser no screens. Then, you are trying to enter a quantity different than what has been allocated. In which case, you must click details and edit the quantity using the Bins or Lot/serial # entry screens and NOT EDIT such quantity in the transaction screen.