instances/underground/test_dome_entrance_lift_01.vmf ??

You should have a "instances/transitions/arrival_departure_transition_ents.vmf" somewhere in your map. Read this, and this for better understanding.

If it's the underground entry elevator you're going to need to put a new trigger in the elevator, directly below where the player's feet will be, and have it start the train. The others don't work.

Someone should add this to the wiki tutorial... And redirect there all the lost beginning mappers.