Collision Not Working with Mathf.Sin()

I had collision between my enemy and player objects. I added in a Sin() for the enemies and now they dont collide with one another. Any ideas?

I found another similar link that seemed to have worked. Not sure what it is, but check it out. This one will let me push the object in the direction I please with the control of the wave.

http://forum.unity3d.com/threads/32044-transform.position-Mathf.Sin