3 Things:
1 - The assassin is your most likely problem. They are bugged, specifically their cloak of shadows skill (I could be wrong about this, but through my own experience I'm pretty sure it is this skill). It only happens to me in certain areas, namely prolonged Ancients battles (NM at /p 8, Hell). Also in Act2, and I think once in Act1, so I'm pretty sure it can happen anywhere. I have no idea what causes it, but it generally seems to be localized to a specific area, or completely random, so if you can get through that area quickly and without using Cloak of Shadows you should be ok.
2 - If this is happening after you kill Andy, go to town, talk to Warriv, click "Go East," then the game crashes, #1 is probably irrelevant. At this point it might be a video-related error (the between-act cut-scenes), or a sound related error. I play with no sound at all, because back in my b.net days my game would crash in Worldstone, and after defragging the ol' harddrive I find my D2 sound file is fragmented beyond control. A complete re-install would obviously help, but simply turning the sound off in-game or using no-sound command is a quick fix.
3 - This is the least likely, but worth mentioning. Back in my b.net days (again) I would get an Unhandled Exception Error very similar to that one. I eventually learned that my CPU was running at an overclocked speed, and that some part of my Hardware or Operating System did not like that when playing games. Reducing my CPU speed fixed this immediately. (Note: I say this solution is unlikely because I was getting this message all the time, and I couldn't play D2 at all.) If you don't know how to go into your bios settings at startup to change this, find someone who does, or at least a very good source (internet, somewhere....)
I have seen 2 or 3 different types of these errors over time, and these are the various solutions I came up with. I know I've had that error before, I just can't remember exactly which one - all those 0's and X's look the same after a while. Hope this helps you out though.