Video codec help for wmp, can't play some video files?

does any1 know how to fix the problem of some of my video files not being able to play with windows media player 11. i downloaded divx installer and codec but still not working. the files that can't play are just "Video Clips", not "Movie Clips", or "Windows Media Audio/Video Files". the error you've probably heard of before is C00D11B1. i don't know why, but before, all my video files worked without this error.