How to cancel Material Dcumented genertaed thru CO11n

Dear Sir,

We have a scenarion where confirmation of Production Order thru CO11n has generated a Material Document . The Material document is generated due to produce of By-Product on confirming of Production Order thru CO11n .

Kindly guide us , how can we delete/cancel the generated Material Document .

We tried to cancel it using MBST but it is not allowing . The error message is as below .......

"Material document cannot be processed. Cancel the material document in the component that created the document.

You can only reverse the goods movement created through the posting of a physical inventory document by carrying out a new physical inventory for the relevant material. You can reverse a delivery effected via Shipping using transaction VL09"

We request you to kindly guide us pl .

Regards

B Mittal