My casle fan world will not build terrain.

Put the summary of the bug you're having here

What I expected to happen was...:
For my casle fan world to load so that I can do things in my world.

What actually happened was...:
My casle fan world does not load.

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. Click single player
3. Click my world
4. Click play selected world
5. It says "loading world" then "building terrain" but the the world does not load, and does not build anything.
3. ...