IsTrigger problem

Hello.

I have a problem with a box collider marked as a Trigger, I want my Player (CharacterController) pass trought it box givving the player ammo, it works perfect when pass the box through sides an below it, the problem is that the player collide at the top of it, I mean when the player comes from top can stand on it. I'm using this a script on the box with these lines at end:

 function OnTriggerEnter (other : Collider) {
     if (other.tag == "Player"){
     taken = true;
         if (isArea && taken) {
             player.SendMessage("Restock", ammount, SendMessageOptions.DontRequireReceiver);
         }
     }
 }

Any help is appreciated. Thanks.