Most themes from Elegant Themes include FancyBox. But sadly without (m)any options to tweak the look and usage of the lightbox. And the fact that FancyBox is already included makes them incompatible with Easy FancyBox.
One user, Horst Weber, has just e-mail me about his experience with making one of the Elegant Themes work with Easy FancyBox. In his case it was the theme called Origin, but a similar method should apply to other themes. This is his way to disable the theme-included FancyBox so that Easy FancyBox will work as intended:
1. Make sure you have the original theme zip available as backup;
2. Go to the WordPress admin Theme Editor and open the themes functions.php.
3. Locate the function that handles the inclusion of script and stylesheets. In the Origin theme it is called function origin_scripts(). In that function, there will be these (or similar) 3 lines: