The old preferences file could cause a crash on opening the app. So go to your USER/Library/Preferences folder and delete the file called MovCationerPrefs and you should be fine.

Also, please be sure to view the movie "How To Get Started" on the website: http://www.slidesnow.com/movcaptioner

You really should see how to use this before you try it the first time. You should use the Start button instead of the movie's play button and don't click the Cue Next button until you know what it's really for. There is also a brief How To Use MovCaptioner file that comes with the app that's worth your time to look at.