It appears that the script that controls the lightbox function, Fancybox, is not loading on the page. There are two versions of Fancybox included with the plugin, one of which may not be compatible with your WordPress install. We would suggest switching to Fancybox version 2. To do so, you will need to access the RPS Image Gallery options panel which requires the Redux Framework plugin. Once activated you should see an option for RPS Image Gallery under the Settings menu. On the options panel, select Slideshow and look for the fancyBox Version setting, then select v2 and click the Save Changes button. Let’s see if that works, and if not, we’ll dig a bit deeper.