A quick look at your website source raised some red flags, since I was noticing none of the Javascript files were loading. I finally figured out that it was tied to W3 Total Cache. Someone else mentioned that Slimbox didn’t work with it, and I think I know why, but the quick fix should be to tell it not to include the plugin. I don’t know how much granular you control you have over it, but I believe if you ensure that slimbox2_autoload.js is excluded, you should be good to go.
FYI, slimbox scripts and CSS are already minified.