Flickrgram not working
"I get a spinning wheel and not images appear"
This is usually caused by some of the image sizes missing from the Flickr Set. To avoid this you should use as large an image as possible to upload to Flickr and it will automatically crunch it to each required size.
If that's not an option, then within the Stack cycle through all the lightbox options "original", "small" etc and preview the selected each time, until you find it works.
"The light box pop-up images don't appear"
This is an easy fix. Just select code type "inline" and preview to see it work nicely :