Is this collider configured as a trigger?
using UnityEngine; using System.Collections;
public class ExampleClass : MonoBehaviour {
public Collider2D coll;
// Use this for initialization void Start () { //Check if the isTrigger option on th Collider2D is set to true or false if(coll.isTrigger) { Debug.Log("This Collider2D can be triggered"); } else if (!coll.isTrigger) { Debug.Log("This Collider2D cannot be triggered"); } } }