Unity says that my script isn't doing anything?

I am working on a building game, and I spawn objects & parent them to a master object. Unity is giving me the

Expressions in statements must only be executed for their side-effects.

error. After a little bit of research, I discovered that Unity thinks my script does not do anything. My script obviously does do something, actually it does quite a bit.

here is the script-

 #pragma strict
 
 var gamemanager : GameObject;
 var spawnedobj : GameObject;
 
 function Start () {
     gamemanager = GameObject.FindGameObjectWithTag("gmanager");
 }
 
 
 function OnMouseOver () {
     if(Input.GetMouseButtonDown(0)) {
         spawnedobj = Instantiate(gamemanager.GetComponent("itemmanager").selectedobject, transform.position, transform.rotation);
         spawnedobj.AddComponent(HingeJoint);
         spawnedobj.GetComponent(HingeJoint).spring.damper.Mathf.Infinity;
     }
 
     if(Input.GetMouseButtonDown(1)) {
         Destroy(spawnedobj);
         spawnedobj = null;
     }
 }

any thoughts on what to do?

*javascript only please, duh

*thanks