I just installed Photopost on my testing site (ubb v7.4.1) and am getting the popup window with no pictures in it as well.. I have tried the fixes above and can not seem to figure it out.
Allen I have checked out your site and love the way you have it working, that is one of the reasons we bought Photopost.
The site I am trying to get it working on is
http://testing.firstgenmc.com/ubbthreadsThanks,
Ian