CO Assignment for a cancelled Invoice

Hi Experts,

Would like to seek your help with regards to the error that we encountered in SAP ECC 6.  Here is our scenario:

An invoice was cancelled last Oct 2014 but the user is unaware that no accounting document was generated.

Below is the accounting entry of the original billing document.  Pls note that based on the document flow the status of the original billing doc is Not cleared.

We tried to release to accounting the Cancellation Invoice (S1) but the message below appeared.  We ignored the error and click Save.

I just wondered why the message below appeared upon saving the cancellation document. In OKC9, we already have a rule that will fill-up the cost center field.  In fact, the original billing document was posted with automatic assignment of Cost Center.

Thanks.