I wondered the same thing. It looks like it is going to play a video and then it doesn't. I'm pretty sure that is the way it is supposed to be, though. It is meant as a flavor screen rather than an intro video (I think).
You can just remove the binkvideo file from the mount&blade folder.
All it does is play a 'commercial' for paradox interactive. No need to be interrupted by that every time you want to play.
I don't know why it doesn't always play though.