Java issues

Put the summary of the bug you're having here
I run the .exe and it only allows me to "play offline". After I select that I go to single player and select one of my worlds but none of them are loading and the game crashes!

What I expected to happen was...:
To play minecraft

What actually happened was...:
It crashes...

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...
3. ...