Plugin works on one website but not another

I installed Easy FancyBox on my beta site when I was testing a new theme, and the plugin worked like a champ. However, now that I’ve put it on my main website it’s not working. Since it works in one place and not another it has to be some kind of switch somewhere within WP that’s causing the problem, but I don’t know where to look.

Could someone please give me somewhere to look to try and fix this?

Thanks

http://wordpress.org/plugins/easy-fancybox/