We had a hiccup with this same installation that caused all the ads to lose connection with their images. All of the ads stopped running. The ads and the image files were there, but had become disconnected. Rebuilt the ads, and they began running again.
This was about the same time I was doing extensive testing to try to get a video ad to run. That problem is still not solved. Not knowing what code WordPress or Ad Rotate use for video controls means trying many combinations. Perhaps one of those caused a server error.