Searchform not working

I’ve just found out that my search-form is not working. I’ve correctly identified the search form class (searchform) but when I click search the aapl-loader-code appears but it doesn’t load results.

The console reports ‘Uncaught TypeError: Cannot call method ‘indexOf’ of undefined’, don’t know if this is relevant.

http://wordpress.org/plugins/advanced-ajax-page-loader/