Postings for account type M ( posting key 99 ) are not defined

Hi,

I am trying to post vendor credit memo KG through FB01 using posting key 21 - Debit Vendor and posting key 99 - Credit Material.

I am getting the error "Postings for account type M ( posting key 99 ) are not defined Message F5204".

The posting key 99 is set for account type material. Is there anything else that need to be configured?

Is there any other way that i can debit a vendor and credit material through FI postings (without purchase order)

Thanks

Sukumar