(1) If it is "Destroy trigger doesn't exist", or some error along those lines, then they likely used WEU custom triggers or EGUI. Those were both popular mods for the trigger editor that added extra GUI functions, events, etc. (or they could be using their own modifications). You can open the map only if you have the mod they used (WEU or EGUI) or if you modify your own editor to include those trigger functions.
Usually, those maps aren't protected, but those functions may act as "soft protection" against users without the mod. That sort of protection usually isn't intentional though (it is often better to destroy the triggers file completely)
(2) If triggers are destroyed/missing, they have either deleted the editor's trigger files or they have replaced it with a blank one. The only thing that matters for the map is the war3map.j, so deleting/replacing the triggers file is usually for map protection/optimization. If the user did that, then the map likely considered "protected" by the author (unless he says otherwise). You can try requesting an unprotected version from the author.
We don't support deprotecting maps or the discussion of it. Make sure the maps in question are the original ones. Even if someone else did the deprotecting, we don't support it.