Entered quantity will make the "Open Qty" field inconsistent with the "Open Inv. Qty" field in the base document; enter a different quantity [Message 439-347]

I am working on sap b1 9.1 pl08 ,today when I add one Goods Receipt PO,system prompt the error messager:

Entered quantity will make the "Open Qty" field inconsistent with the "Open Inv. Qty" field in the base document; enter a different quantity [Message 439-347]

,how to fix it I don't know .