If you're getting that error it means the spawner is working but the NPC has some error. Do you have many vehicle/NPC files on your base folder? It could've been overrided and hence the x-wing doesn't spawn.
As far as I know, the only way you can do that is by doing a script that tell the NPCs to not follow you.
In one of my maps I turned rebels into enemies by applying the following script to them:
set ( "SET_PLAYER_TEAM", "TEAM_ENEMY" );
set ( "SET_ENEMY_TEAM", "TEAM_PLAYER" );
set ( "SET_BEHAVIOR_STATE", "BS_DEFAULT" );
set ( "SET_LEADER", "NULL" );
set ( "SET_CHASE_ENEMIES", "true" );
set ( "SET_LOOK_FOR_ENEMIES", "true" );
SET_LEADER "NULL" makes them stop following you.