Hi arimanuel,
My best guess is that the conflict is caused by a plugin or theme. Try deactivating any other plugins you have. If the problem persists, try switching to a stock twentysomething theme. If that fixes it, it’s a conflict with your theme.
I noticed that your site is enqueuing an old version of jquery, version 1.6.2. That means something (a plugin or probably the theme) is overriding WordPress’s default version of jQuery with its own. This is a very bad idea and will cause incompatibility problems with loads of plugins. Here’s Pippin on why loading your own jquery is irresponsible.
Track down the plugin or theme code that’s causing that and I’d guess you’ll find the solution. I can’t be sure though.