The script attached to this event fires when an attempt to open a door fails which could signal another event to spawn creatures to investigate the noise, notify the opening that they need a key or the door cannot be opened by normal means, or a variety of other things.
A creature failing to open a door, due to it being locked somehow.
GetClickingObject() will return the object which tried to open the door.
This mainly is useful for feedback - or a special kind of key, or triggering a special "locked door" conversation. Unlike On Open or On Closed, this will fire when they cannot open a door. It doesn't seem to be the case that you can force a door to stay open - therefore, any door that has this event fired must basically be closed already. For this event to fire, the minimum requirements are that it is open, and is locked (GetIsLocked() == TRUE). These two should always be true when the script fires. Note: Whenever a door is locked, and thusly this event fires, there is always a clunk, handle rattle and so on, even if you allow the door to then open. Adding a conversation (do you wish to use XXX to open this door?) helps make it a little less odd.