FancyBox doesn't work with GRAND Theme

I used the FancyBox Plugin for many websites and it worked always like a charm, but on this page i can’t get it working. Sample Page
So far i tried to disable all other plugins, delete other scripts, which are loaded with the theme (eccept jQuery), create the link manually, but no chance.

So, i really need the Plugin to load several pdf datasheets in a fancybox, like here: Verleih

In the sourcecode i saw, that the script is loaded etc., but i cant find the error.

Someone can help me pls?

ty

https://www.ads-software.com/plugins/easy-fancybox/