When I try to open my map, the editor says this...and crashes.
I tried to look into the map (.j) script and i found function DestroyTrigger. I deleted this one, but WE started to say "Function does not exist: DestroyTrigger" . I don't know JASS and this was the only thing I'm able to do.
Did you used WEU or another third party editor? Some their GUI triggers are not in standard WE [like Destroy Trigger] so trying to open map created in one of those will cause standard WE to crash.