Is it possible to throw an error in blueprint?

First of all, it might be better to have your trigger be part of the door blueprint and thus make suré it’s Always there. Second, inside your door blueprint add a spawn player character next to it so it will open. Add a print string for when it opens. Inside the string would be the BP name. If done correctly you would get a list of strings of all doors that work. You can easily isolate the doors that don’t work that way.