When I enter singleplayer it sens me back to the title screen.

I had alreadty had minecraft 1.4.5 for a few days, and one afternoon, I was logging into one of my creative singleplayer worlds. I got stuck on the screen that said "Chunks loading" or something like that. Then it sent me back to the title screen.

I had mods, so I force updated minecraft, but that didn't help.

When I was stuck on the title screen I waited a few minutes and minecraft crashed.
I attached the crash report.

Steps to Reproduce:
I don't know how to reproduce it, I can't NOT reprodce it