Sounds like the file your trying to get to play is buggered. Try opening it in virtualdub see what that spits back. GSpot while excellent for .avis will not tell you much for .mpeg and .asf,
afaik that support hasnt been added to it yet.
Also, BSPlayer shouldnt be able to damage a file, it should only be reading the file.. something very wrong is happening if its writing to them.