'Sales shipt lines' cannot close

Hi Pple I encountered this error msg when I tried getting shipment lines for charging items: ‘Sales shipment lines’ cannot close because the system is currently working. This is not the first time I encountered this msg but the second msg that follows up is my first: Item Shipment Entry No. must not be 0 in Sales shipment line document no. = XXXXX, Line no = 10000. Anyone can help? Thanks in advance.