SD BILLING(CREDIT MEMO) AGAINST PGR

Hi

      I have created sales return order and PGR with Item Category REN (Billing relevance-Delivery related billing). After that  I am directly trying to create Credit Memo against PGR instead of regular process(Credit memo request and Credit memo).  But when I create Credit memo in VF01 against PGR it is showing error log(Document not relevant for Billing). Kindly help me.

Regards

Ganesh