Perhaps make it a placeable transition rather then a goblin npc that seems to get killed nightly by npc nightrisers, angry dwarves or whatever. There is no way thru it from the opposeing side. Unless this is intentional. Clicking on the transition "footprints" does nothing to help the situation.
Same problem at the main gate right now(into gobsquat), just get "locked" message, would suggest the same solution. Unless of course, it is meant to be such.