i buy the original version of the game,and i know what your talking about,i have the same problem,when you exit the assasin office just do it slowly,dont run.
they have a lagspike problem near that area and thats crash the game.
The pirated pre sell version was with a corrupt Jerusalem file. (only the Russin version worked somehow)
And a lot of BTD crashes occured during the game.
The legal version got rid of all problems, but there are still some times, when the game crashes.
Especialy on older machines, when the games sucks up a lot of ressources.
Maybe you can try to lower your details. If you've got a good machine, try to set the sound enhancement of the Direct X tools to "off".
Played the pirated version and bought the game, when it came out.
Thats exactly the kind of good games, I want to pay for.
Now I am thinking of Far Cry 2....uuh I want my money back!
Anyway , I'll say it now and probably say it again sometime , where I live in people don't know what an "original game" is. I really don't feel like traveling 600 miles to the capital to get the original copy of the game.