Places menu corrupted

Referring to this discussion I locked all the panel and menus in my machines, but users are unpredictable and in one pc I have this problem: when I click on "Home", in "Places" menu... it launches VLC with some .mp3 or .mp4 file.
Definitively I can't understand how it can be, but I neither can't understand how to fix it.
Someone can help me?

Check System, Preferences, Personal, Preferred Applications. On the System tab, look at File Manager.

Thank you MDooley, you was right.
In preferred file manager there was VLC instead of Caja.
That is weird, how could happen this?
Thank you again.

Edit: preferred applications is not accessible from menu and menu in not editable.