Updates to Left 4 Dead 2 have been released. The updates will be applied automatically when your Steam client is restarted. The major changes include:

Left 4 Dead 2

• Fixed case where game failed to launch in certain machine configurations
• Fixed bug where a burning witch could get into a state where she’s invincible
• Fixed bug where bots would not shoot at Jockeys and Chargers while approaching to save a teammate

Well those certainly sound like worthy fixes and frankly, I’d hate to be in a situation where there was an invincible burning with a Jockey and Charger prior to these fixes.

In regards to the certain machine configurations we can only guess it had something to do with either multiple monitors, graphics cards or non-standard storage solutions.

So get out there and BURN THE WITCH! You could at least survive now.