invoice by sales order (transaction notification)

I do need to develop a transaction notification to block invoice if it not have sale orden
mi code is

-------------------------No es posible Facturar sin Orden de Compra


IF @transaction_type IN ('A','U') AND @Object_type = '13'
BEGIN
IF (SELECT COUNT(BaseType) FROM INV1 Where DocEntry = @list_of_cols_val_tab_del AND BaseType <> 17) >= 1
    set @error = -1
        set @error_message = N'No es posible crear una Factura sin Orden de Venta'
    END
END

and the block is correct but I can't copy partially the sale order