hi,
it was already mentioned for Prefs > General > Fake Check > Custom Browser, but same applies to Preferences > Directories > Video Player:
an app typed in here is not found, an app selected with the supplied file dialog results in a ref to the .app bundle which does not work either. A good working method is to select:
open -a firefox (or similar)
and
open -a VLC (or similar)
maybe you can fix it that way.
btw: "Create backup to preview" doesn't work. it just doesn't. (or dubbing the file is incredible fast)
... m2kio !