If you haven't yet, get a tutorial on dynamic clothes. (PhilC has a free one on his site, I don't have the link handy but it would be easy enough for you to find.) I have been having a similar problem in which I was trying to simulate a skirt colliding against V3 and stockings she was wearing. For some reason, the simulation freaked out because of the collision with the stockings, and got stuck on a frame. I unchecked collision against the stockings, and the simulation worked fine- except one small part where the stockings show through the skirt, but for now I'm going to take care of that with a transparency map to hide the part of the stockings that aren't supposed to show through. Just a band-aid solution, but it will work for my particular pose. You might try something similar until you can figure out a better solution. Just collide against the guy but not the pants. If any part of the pants show through the coat, you can probably take care of it with a transmap to hide that part of the pants. A band-aid, but it might work for you to get your render finished.