I am working on WordPress 3.5.1 on a dev site, and a live site. I was able after many tries to change the SideOffer background image on my dev site, and the client approved it. Now I'm trying to do the same on the live site and cannot get the background image to change. Each time I upload an image, or select it from the Media Library, nothing happens, and the horizontal pixel position box value goes from -500 to -NaN.
Any idea what's happening?