Trigger and Collider Issues

I know that there are certain formulas for colliders as in some work with others and some don't. I have checked the unity physics page ie: Link. I need some clarification on the combinations for a project.

I have a very simple script here, but OnTriggerEnter is never returning true. I believe this is due to an invalid combination of triggers/colliders. The script is attached to a movable gameobject, which has a BoxCollider and a SphereCollider set to "isTrigger". On the other gameobject i have a BoxCollider. None of them have Rigidbodys. Any help on why OnTriggerEnter is never returning?

Some Code:

 function OnTriggerEnter(trig:Collider){
     if(trig.tag == "Building"){
     Debug.Log("Building");
     building = trig.transform.parent.gameObject;
     buidlingScript = building.GetComponent(Building);
     build = true;
     }
 }