Windows 7: media center crashes to xbox360 desktop when playing some movies

I have windows 7 64bit that connects to my 360 via cable/router. For some strange reason some of my movies that i try to play makes media center crash to the 360 desktop with no warning error.

The video files are .mp4 and play on my windows media center. Some of these movies used to play ok and some still do but its like a random occurrence as to which movies it picks to play and what not to play yet its generally the newer movies i put into my movies directory.

If i put these movies onto a usb they play perfectly on the 360