FM 19 Editor: Error In Nation Rules: unknown type

I have been trying to activate the lower tiers in South Korea and add the real life promotion system they have. I have spent 3 hours getting several errors regarding dates and not being able to get enough teams and I have managed to get past all them. But I have just ran into an error I can't work out.

I test the rules of all the 5 leagues and the first 4 divisions work fine, but as soon as I test the 5th tier, it get's to about November 2018 in it's simulation and then shows an error stating "Error in nation rules - unknown type". I have attached a screenshot


Does anybody know what this error means?

I know a lot of people are annoyed over the amount of bugs in the editor this year and people have raised this issue for SI. It seems like they don't really care, tbh.

You'll probably have more luck if you ask here.