Collision triggers 2 events

When I'm colliding my player with an object to pick up, it causes the OnTriggerEvent to operate 2 times.

I have only one Box Collider on my pickup objects.

How can I fix it?

 void OnTriggerEnter(Collider other) 
 {
     if (other.gameObject.tag == "PickUp") 
     {
         Debug.Log ("Player picks up an object");
         other.gameObject.SetActive(false); // disables touched object
         score = score + 0.5f; // workaround over double triggering
         SetScoreText(); // updates score text, nothing special
     }