Image Display issue

I am having difficulty with several images throughout a presentation. I am using an oval, which has been inserted as a png to direct users’ attention to a specific portion of the screen. The image is a timed animation that enters with the wipe effect. It appears on top of another image. My problem is that only a portion of the oval (the image on top) displays. Part of it looks like it is below the other image (which it isn’t). I’ve used this feature successfully on other slides in the presentation. However, on several slides the feature is not displaying properly when the presentation is published. To complicate matters, a co-worker tried to help me out by publishing the file for me. She had the same results when publishing on a desktop PC, but the file published correctly when published on a laptop.