Old reservation not deleted

Hi,

There is very old sales order which is completely closed. all the line items with respective delivery quantities has been

delivered and also invoiced.

But for one material in CO09 (Availability check) system is still showing reservation against that order if we checked that

material nothing quantity was left to deliver. because of which for current orders system is not allowing to do deliveries.

why it is happening ?

How to cancle that delivery?

because in CO09 there is no option for manual deletion.

regards,

Anup