Buffer overflow blocked???

Gentlemen: I made the mistake of downloading "Windows Media Player 10" and could not get it to work. I then reverted back to "Windows Media Player 9" and it worked fair but not like I had it installed initially before the "Media 10" was downloaded. I have some movie clips stored on my hard drive and as soon as I try to use "Windows Media 9" to open the movie, I get a "Buffer overflow blocked" box and that ends trying to open the movie??? I can play the clips on "Media player Classic" with no problem? How is "Windows Media Player 9" fouling this up it didn't happen prior to introducing " Window Media 10"??? How can I make "Media Player Classic" my Basic user? Can I delete "Windows 10" with no after problems? Ronnies