My mp4 file won't play if there's a subtitle file in the same folder. It was working earlier but I was messing with the directvobsub filter trying to change the font size. Now the file won't play.
If you have CCCP, go to CCCP settings, 2nd page, do a reset settings there and everything should be fine. If you don't have CCCP either get it or read a lot on how to correctly configure the individual components you have.