I have an extremely frustrating issue with Java. The computer has Windows 7 64-bit. The website the user is trying to get to is catalog.comstarsupply.com. When you add something to the cart, a picture of gears and a loading box comes up and doesn't go away. If you click to go right to the cart, it just sits there. The user has no issues with any other sites. I even went to a site that tests java, and had no issues. I've tried Firefox and chrome...I've tried uninstalling all browsers, including IE, uninstalling Java, rebooting, and reinstalling just IE and java....still the same issue. I tested the site from a few other computers on the same network and can access it just fine. I also tried IE 7, 8, and 9.
When you click to add to the cart it is redirecting the browser to a secure page, so the problem may be related to access an https page, although that's so common it seems unlikely.
It sounds to me like your running into a bug with their website. I'd contact the company and let them know what you're seeing and see what they say. If the error is on their end (at their servers) there's nothing you can do with the browser to fix it.
Doug