Object ignore collider with another - Please Help

So I have tried the following as suggested on another thread.

 void OnCollisionEnter(Collision collision)
    {
        if (collision.gameObject.tag == "theobjectToIgnore")
        {
            Physics.IgnoreCollision(theobjectToIgnore.collider, collider);
        }

I'm trying to push a ball through a barrier, the ball is supposed to go through but not the character. The object is named Ball and the tag is also named Ball. So my script is as follows:

  void OnCollisionEnter(Collision collision)
      {
          if (collision.gameObject.tag == "Ball")
          {
              Physics.IgnoreCollision(**Ball**.collider, collider);
          }
      }

the second ball though is red and it is not being detected via typing... can anyone help me?