you may have corruption, files, preference or even the app.
Try another m2v file (make sure the file is not a transport or program stream, audio and video in the same file, if it is that is your problem, dvds need elementary streams, just the video)
If that file works, it is the first file that is the problem, if it still doesn’t work, trash pref, if that doesn’t help re-install DVDSP.