Yes, as I suspected you have other JavaScript related errors on the page. Probably something related to your template customization. Using Chrome, I looked in the console and saw this:
Uncaught TypeError: Cannot set property 'quantity' of undefined
www.maxmusclestoreonline.com/:304
Uncaught TypeError: Cannot set property 'quantity' of undefined (index):370
Uncaught TypeError: Cannot set property 'quantity' of undefined (index):475
Uncaught SyntaxError: Unexpected identifier memo.php:1