Lightmap index error

I'm getting this error:

 "Lightmap index must be less than 256."

That's all it says, it doesn't point to any objects when I click the error either.

I LoadAdditive a scene with a Terrain in it. When I need to load the next scene, I delete the Terrain gameObject. After exactly 9 times, every time, I get that error. Any ideas?

Thanks.