I keep getting this error when starting up the game, and I can't get it to work for some reason. I suppose there is something wrong I've done to make this happen. Could someone explain, please?

https://edge.hoi4modding.com/mod/38166

this is my mod.

I think that if every province isn't controlled then you might get that error. I would suggest that you create a placeholder "country" that holds the unassigned territories temporarily.