All thumbnails show up as grey boxes with wowslider slideshow

Question

I'm trying to figure out why ALL of the thumbnails show up as small grey boxes instead of the thumbnail images. The slideshow images all show up but the thumbnails don't show up at all

Wowslider is being used for the slideshow

Here is the URL to the web page: http://lbschoolbonds.net/middleschool1.cfm

Can someone please help me figure this out?

Thank you so much!!:)