I must say I lolled while watching the video xD That obviously is a rigging error (in other words a problem with the animation, bones of the animation). If this is a model that you compiled and exported, then the only reason I can find for this is something that I once had experienced: Make sure you have not 2 bones with the same name. This causes tremendous errors in the animations and makes them totally bugged. If not, then there is not much you can do but find another model.
There's your problem. You're gonna have to completely re-render the model i think. You can't rip models from all games, or silly things like that happen LOL. I have no modeling experience, so joris, halp.
It's possible to work, but it won't always. I'm pretty sure Dark Messiah uses a slightly modified source engine, which is why your animations are freaking out.
