Stucked at billing Information section on checkout page

Question

Every time i try to continue the testing procedure for the checkout page i get stuck at the billing information. It says loading, but does not continue for the next section.

1. I'm using one page checkout
2. when i click inspect element and go to the network tab it is showing 1 js file which is jquery-1.10.2.min.map
3. The error returned is: "Uncaught TypeError: string is not a function" in a js file called prototype.js
4. I'm using magento 1.9

Anyone can help on this ?? My website is www.925sterlingsilver.com.au

Thnaks in advance