Yes, I had the same problem. This happened when i tried to play 2 videos at the same time in separate screens. One of the videos would play all the way, the other would only play the first 10 seconds or so, and then loop back to the beginning. It was about 5 minutes and 54MB. I was told it's because the computer can only open one instance of windows media player, but if that was true, how did it even open the second video at all?
What is the size of your video?