I had been having trouble with getting the slider to work in various versions of IE, particularly IE8, but I figured out the problem and wanted to share it here for anyone having the same problem.
The slider was not showing any images (just the red "X" in IE), nor was it showing any loading animations, etc. at all.
The problem, which only breaks the slider in IE, not Chrome, Safari, etc, is when you don't have an image set for one of the slides. Each slide needs a featured image set to work.
Hope this helps someone.