Topic: Only 2 X's show up in gallery page

I installed the simpleviewer on one of my sites and it works well.... but when I went to install it on another one of my sites, all it gives me is a small X (where the thumbnails shoud be) and a large X where the large picture should be. 
I have gone over and over the code and can not figure out why it doesn't work, especially since it worked fine on my other site. 
Can anyone lead me in the right direction of what I should check or do next?
Thanks for your help in advance.

--terri