Whenever I press play in the Minecraft Launcher 1.4.2 the loading bar almost reaches the end but when it does the launcher closes, another window briefly opens then closes and the launcher is re-opened.

What I expected to happen was for when I clicked on the play option in the launcher, Minecraft, would open and I would play.

What really happened was that I pressed play and the launcher closed, another window briefly opened then closed and the launcher re-opened.

Steps to reproduce this bug:
1. Open the Minecraft Launcher 1.4.2
2. Click play
3.Wait for Minecraft to open
4. Minecraft won't open