I've found you can get a BK warning if you make a REALLY big "loss" in one particular week, even if everything got paid as it should. I mean like if you spend $100M on orders or something. Maybe there also need to be a loan not paid or something, I'm not sure. (Remember, it's not just loans - you also have salaries, marketing, alliance fees, fuel contract fees, missed maintenance, failed training fees that MAY cause problems). But anyway you can just ignore it and it will go away after a week or so. The modelling in financial system can be really annoying but I understand it's all being revamped at some point.