photogallery popup problem

Hello, I am using Sigplus image gallery plugin for my site based on Quark template and I am facing a strange problem. The pictures are shown but when i click for the preview another window or tab opens for the preview and don't show the popup lightbox...
Please could you advice me in this problem? Thank you!

Could you please provide me with a URL to your website, either here or via PM (click the “Private Message” text underneath my avatar) so that I may analyze it? It is a lot easier for us to diagnose issues when we have a live site to examine.