Firstly, did you download the files with the 'downloading in parts' option? By which I mean did u open the torrent and tick what u want to download and untick what you don't want to download?
Because I also got the same problem, I used the 'download in parts' option with which u can download what ever you want first from the torrent file by ticking and unticking respectively. I was downloading Prison Break season 1 torrent, I decided to download the first episode, downloaded, worked, downloaded the second episode and that did not work, gave the same error as your files are giving, I tried working the file in every possible media player but to no avail, finally I just redownloaded the file and voila, it starts working.
I'm really freaked out by this problem because its never happened before.