Hatikvah

Hi I'm trying to follow the Geck tutorial to build my own vault however after placing 2 large rooms, 4 small rooms and halls adding the clutter I did the navmesh, saved came back later loaded it and the rooms / halls vanished leaving clutter and a staircase. Putting this down to my crash happy geck I retried it with an earlier save. But after every navmesh or optimization, loading the vault in the render window causes the rooms to vanish :confused: Thanks for any help,