exception; java.lang.ClassCastException: bit cannot be cast to fm

Put the summary of the bug you're having here

What I expected to happen was...: the game to load up my newly created world.
Describe what you thought should happen here

What actually happened was...: the game threw the following exception: exception; [java.lang.ClassCastException: bit cannot be cast to fm]
Describe what happened here

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...launch newly installed game
3. ...create a new world
4. ...select newly created world and click "single player"
5. ...that is when I receive the exception