Hi Dinesh,
I am agreed with Dieter,
Please check the BOM materials costing date,
and also please drill down your checking criteria.... in your case check backward detail. e.g.
Item code which you are going to sell.
Lot qty which you are going to sell.
Production order no. from which this lot qty generated
and in the same production order check the estimated material.
and check the Estimated material Cost price calculation date.
I am damn sure that estimated item is not as per Bill Of Material. so check estimated item and its date. than u will definitely find the exact item which have cost price calculation is after sales order date.

Thanks
Sirf Hum