No renderer.enabled=false on grouped GameObject

Hi everyone, if some of my Gameobjects are grouped in the hierarchy "GameObject.renderer.enabled = false;" is not working. I just want hide some objects if the mouse is over an object. Is there anybody who can explain that to me? Im still a beginner on Unity and in some points I dont understand the software. Here is my code snippet:

 #pragma strict
 
 var group1 : GameObject;
 var group2 : GameObject;
 
 
 function Start() {
      group1 = GameObject.Find("GameObjectGroup1");
      group2 = GameObject.Find("GameObjectGroup2");
 }
 
 function OnMouseOver() {
     group1.renderer.active = false;
     group2.renderer.active = true;
 }
 
 
 function OnMouseExit() {
     group1.renderer.active = true;
     group2.renderer.active = false;
 }

it would be great if some of you have me some answers. thanks!