[valych]

Most likely (if coordinates of teleportation point are right), objects of your interior can't manage to load for player in time which causes him to fall down. Try to set Z coordinate to "Z_value + 1" (or even 2) in SetPlayerPos function.
In case if you cant even see objects of your interior, check whether they are created and then double check the correctness of coordinates where a player is to be teleported to.