Another poster above has suggested this is memory related and I am inclined to agree. If I am very cautious and restart the game every 40 minutes (or as soon as I see RAM usage go above a certain level) then I can seemingly avoid any crashes entirely. That strongly suggests that some condition is building up the longer the game is running.
It is indeed a memory leak causing the issue. On a 32 bit system, no app can allocate more than 2GB of memory for use. A memory leak is when an app is using memory but not giving back when done, so it takes more. Because this is in direct violation to the laws of the kernel, the game is forced to crash. OS > Application any day! This is why we have moments when we *think* we're about to crash but don't, and also when we actually crash, but don't expect it. The difference on a 64 bit system is that its taking a lot more memory, and not giving it back. Taking into consideration what the OS requires to live, what the machine reserves for use, and playing this game for a solid 2 or 3 hours...I'd venture to say a good 32GB of memory may be needed. Also, the latest nVidia drivers (2013) aren't compatible with the game. You will get an error message. Hopefully a fix is incoming with this expansion...I've never seen a game where I pay a sub get an expansion BEFORE attending to its bugs that admits it hasn't found a fix for yet. Strange.