Very weird error when adding an item to cart

-- url of the page with the problem -- : thegreenbookdc.emorydayclients.com/buy-now.html
-- HikaShop version -- : 2.3.3
-- Joomla version -- : 3.3.6
-- Browser(s) name and version -- : any
-- Error-message(debug-mod must be tuned on) -- : 404 when clicking Checkout after adding an item to cart

Ok so I get a very strange error message when adding a product to cart. If you go to thegreenbookdc.emorydayclients.com/buy-now.html and add one of the two products to the cart, the window pops up, which is good. The problem is that clicking on Continue Shopping does nothing and clicking on Checkout gives me a 404 error at the following URL:

thegreenbookdc.emorydayclients.com/jQuery.colorbox.close() ;

Any help would be appreciated. BTW I can't update versions until the site gets migrated to the client's server because the dev server has problems with the new version (it's the server's config causing problems, not your software).

Thanks!

Cynthia