Okay, I have this happen once in a while,and I figured out why.
What happens is, when I launch the game, it goes black for a second or two, then closes back to my desktop, and I have to restart the game.
I'm on Windows 7 64 bit RC atm.
It only does this when I select another program to bring up from the task bar, like Firefox for example.
So, if I hit play, to launch the game, and before it launches, select Firefox to re maximize, for whatever reason, when the game begins to start, it stops, and i have to re-log and everything.
...just thought I'd post a reason to a potentially major(in terms of annoyance) problem.