I am having the exact same issue. I have a website that was originally J1.7 and was then upgraded to J2.5. When that upgrade was done was when the popups stopped working. I haven't had any issues with any other components or modules and their popups in the backend.
For further testing, however, I installed a clean installed of J2.5 and installed this module and the popup working just fine.
So I went to the extent of disabling every single module, component, and plugin on the site that isn't working to just have core elements enabled and still popups do not work.
I have also uninstalled and re-installed the entire module with absolutely no luck whatsoever. There is clearly some kind of conflict with the module and something else on the site, but I can't figure out what.
Not working site:
http://screencast.com/t/cHg3aJyc29atWorking site:
http://screencast.com/t/davsewOcYTPLEASE HELP! We launch in a day and I can't get the images updated that need to be updated. I'm so stuck we may have to rebuild the entire site to get this one little function working. Very frustrating.
PS. I am using the latest module install. Just downloaded it this afternoon.