jquery slider not working with post thumbnails

Hi,
I’m using a theme called brave-zeenat on my website: http://www.shannon-rae.com. It’s supposed to have a slider on the front page that shows posts from certain categories and a thumbnail, but the thumbnail image won’t show up! Everything works except the pic- the text works and the animation slides when you click it. I just need help with the picture!

The help file says to put a custom field in the post called “Thumbnail” with the url to the image. I tried linking it to “sample-slide.jpg” that came with the theme. I also tried uploading the picture to wordpress and using the url that they gave me for the image…. I don’t know what else to try! Please help!!