Put the summary of the bug you're having here

What I expected to happen was...:
I expected the level to open and work as normal. I had been working on an extensive map with command blocks.

What actually happened was...:
The game will open fine, and opens other levels fine, but this level produces an immediate crash.

Steps to Reproduce:
1. Open the level file.
2. ...Crash.
3. ...Crash report.