Just as a heads up for anyone else who might be in a similar situation as I was. I got this warning after adding a whole lot of foliage to my level and re-built everything. While painting the foliage, I had the cull distance set to 0 so I could see all of the trees from high up in the air. As soon as I set the foliage max cull distance to 40,000 the error message went away.