Hello to all.
You are not alone if you have software glitches with your game. I too suffer from the same problem. In my case the start of level 15 'The Infernal Machine' doesn't work. When I climb to the bottom of the ladder I can't get out of the pit because the giant cog/lift is missing from my game.
I've contacted Lucasarts help dept and I've tried all of the updates. They sent me a save file but that also had a problem that prevented me from continuing any further.
I doubt I'll ever see the end of the game as I keep finding new problems. If any one out there has had the same problem then I'd be interested to know how you solved it.