Why does this trigger not work?

I have flagged my created item as "horn" and in items the horn is set as a useable item.

Event:
Unit - A unit owned by Player 1 (Red) Uses an item

Condition:
(Item being manipulated) Equal to Horn
(Region 013 <gen> contains (Hero manipulating item)) Equal to True

Action:
Trigger - Turn off (This trigger)
Sound - Play TheHornOfCenarius <gen>
Item - Remove Horn
Unit - Make Frosthowl the Ancient 0439 <gen> Vulnerable
Unit - Unpause Frosthowl the Ancient 0439 <gen>

This doesn't work at all though, I take my hero to the region "13" and use the horn and absolutly nothing happens.

Trigger tags please.

It must be a charged item for that to work. Make the item summon as a work around, and detect the summon (then remove the summons).