I also just had this issue today, but luckily managed to fix it quite quickly.
My issue was giving me the same error, but I had only been toying around with local height fogs. Removing them before the level crashed saved me 
I also just had this issue today, but luckily managed to fix it quite quickly.
My issue was giving me the same error, but I had only been toying around with local height fogs. Removing them before the level crashed saved me