sales order stock doesn't exist for serial number management material

Hi all

Material 8003-30-65210 is a in-bound production material for my company, it used to be a material without batch or serial number management. Yesterday I made it under serial number management and used IQ01 to create serial number for the existed inventory, at the same time I also activated the equipment view. Finally I can find the equipment & serial number through MMBE-Equipment & serial number.

The problem is that when I want to post a goods delivery to customer with VL02N, after I add the serial number and then I click post and issue, there is a error which shows that sales order stock 11015727 does not exist. But there is unrestricted-use stock in the warehouse.

Can anybody help me? Thanks a lot.