Option Combination Locks Up Cart

When I select the first option combination for one of my products, the cart sits at the “Loading” prompt. The user can’t move forward. It doesn’t always happen, but happens frequently. Screen shot attached.

Here is a link to the product where the behavior occurs: [url]http://appogee.com/store/index.php?dispatch=products.view&product_id=29786[/url]

Thanks for your help.