After giving billing block in sales order still able to bill the document.
I created one milestone billing and assigned to item category and sales document type.
in billing plan i had given billing block and also 2 proposed dates.
now when i am creating sales document system is coping all the information from billing plan.
it has billing block also
but when i am creating billing document with referance to sales order its not blocking.
in copy control i made the same setting as we had in credit memo request to credit memo.
on credit memo request it is working properly but in my order its not working
so can any body will help where i was getting wrong.