[Clipping Mask not Working]

In the past all I had to do to clip a picture a clipping mask was drag it underneath. Now, when I try, it doesn't work. The mask is a png. I've attached a screenshot. The very large picture is dragged under a mask. You can see that in the right hand column. But the picture is not clipping to the mask. I've included a screenshot of the mask as well. The weird thing is that this has worked on other templates that I used. Just not on this particular mask.