Why do modals only work on certain pages?

Not sure if this support is only for WPMU products. I've got visual composer installed and the addon pack for it, which provides modal functionality. I've a sidebar with two modal buttons refer a friend and contact etc. They work on some pages, but not on others and I can't seem to find what differences there are on the working v non working pages. Can you help?

http://rosiebellington.com