Not sure if this has to do with everyone's situation or not, but in my case the game was hanging every time it said "Awaiting Game Start (0)". I tried setting the game to bare minimum video settings and numerous other attempts. I had the latest video drivers. What I was doing was starting the game, changing a video setting, loading my saved game, and then attempting to enter the mission from the strategic view. Nothing ever worked. As a last ditch effort, I tried starting the game, changing a video setting, exiting the game, restarting the game, and then loading my saved game. This time it worked!
So, in my case at least, the game requires a restart after any video setting change before trying to enter tactical combat. Maybe this will help the coders find the problem.
This is running Windows 7 64-bit with a Radeon 5870 1GB video card.