Thanks guys apprciate for your response.
Alternatively its my thought, if we can make the billing date as mandatory in VF11 or make it as current date by default?
Since the issue is users are trying to delete the deliveries after invoice cancellation with out accounting clearance which leads to havoc at the finance side to adjust the same. As ours is an consumer project and we will not recommend giving credit/debit note to the cusotmers.
Thanks,
Satish