Mike:
I just was exploring the difference between PostNuke and PHPWebSite which apparently is what you used. I suspect I may've found your problem. Their website at:
http://phpwebsite.appstate.edu/
says: "Due to the large load we have been experiencing from people linking to theme images on our server. We would like to remind everyone to edit their stylesheets and themes. If you modified the default 0.8.x theme and did not update your stylesheet or links. You will notice your site is blinking black box!
Please edit your stylesheet and theme to point to your website. The theme and images in question have not existed for a couple of months on our site but we still receive many hits. This only slows things down and hurts the community as a whole so please update your theme if this issue exists."
Let us know if that helps.
Sheila