I did search and found an issue similar to this, but I think this one is different, I'm not sure why.

What I expected to happen was...:
I expected the game to open so I could check out snapshot 13w18b.

What actually happened was...:
I clicked 'play', the game began loading as usual, got up to the Mojang logo, turned back, and closed. I had 13w18b selected, the launcher said 'Minecraft Launcher 0.7 (Dev). It also said the snapshot would be installed. It appeared to finish downloading. The launcher still says it will be installed. After restarting, the launcher says it's up to date, but the game still closes.

I don't even know. The crash report is attached.