After applying the 3d camera tracker I right click between three targets and select "create null and camera", this creates a null object correctly aligned with the selected target and a camera, however, when I scrub through the timeline the null object is not tracking along with the selected target in the scene, it just stays in the one spot on the screen. It only just started to have this problem, it had been working fine before and all of a sudden its not working. Is there a way of fixing this? Did i accidentally deactivate the feature some how? Cheers Luke.
I'm not sure I follow your description. When you say the null does not track with the target, that would be correct if the target is something that is moving in the scene because the 3D camera tracker solves for a moving camera solution by analyzing the change in parallax of fixed geometry in the scene. IOW, it's looking for things like buildings and roads and rocks that do not move. The camera is then added to the scene and 3D object you add to the scene should stick to the plane in the scene where it was placed. In other words, if you stuck a null to the sidewalk or to a wall, the null would stay stuck to the wall.
If, on the other hand, you want to attach a null to something moving through the scene, like someone walking or a car driving, then Camera tracking is not the right tool. You need to use AE's motion tracker or Mocha to track the moving object inside the scene. That tracking data is what you must use to attach a null, or a layer, or text to something that is moving through the scene.