Dear,
Please check the BOM of you material in CS02 has component with cost relevancy. Component should not be a bulk material.
Check the BOM usage 1 relevecy for costing in OS20 and Check whether the costing relevancy indicator is set defaulty in OS21. And BOM in component details in CS02. Also ckeck the validity date of alternative BOM 1.
BOM status should be active.
Please check the costing view in material master for Lot size. This is just information message.
Also refer the below discussion,
http://scn.sap.com/thread/1113768
Regards,
R.Brahmankar