I had a few issues displaying the virtual slide box image contents on an old Safari (5.0.5) browser.
I originally built and setup the WordPress site including this plugin using the latest Firefox (v29.1)etc and I periodically checked the latest Safari and Chrome during the build.
The plugin was fine on all newer browsers, but not the old Safari. The older browser displayed grey boxes where the images should have been.
It looks like I've resolved the issue by rebuilding or relinking each background image by working from within the old Safari 5.0.5, so thought I'd share that; just in case.