Problem with creating Billing Document

Hi,

i am in process of creating a Billing Document for SalesOrder.by gong to T- Code VF01 for creation of Billing document i am passing the values in required Fields.in Field SD Document i am passing Sales Document Number(0000000001) which i created for sales order.while saving it it is not showing any billing document.any body have idea what is wrong. thanks in advance.

Thanks

Kiran.B