Procedure KOFIAB Acct determination missing

Hi Gurus,

After creating the billing doc, I'm able to save it ok, but it remains open and I get this message, after going to environment - acc determ. analysis - reconciliation accounts " message 302 Procedure KOFIAB Accnt. Determination missing (Reconciliation Acct). VKOA is fine and I have no clue what's going on. Can anybody tell me how to find the solution?
Thanks