Problem with Marketpress. The shopping cart is not updating for some people.

Some people are having problems with the shopping cart on my website.

http://assault-knights.com/

The shopping cart works fine for me. And from what I seen most other people. But a couple that I have been trying to help out has been reporting when they try to add a product to it from my product page

http://assault-knights.com/store/products/

It does not update there cart. I have already told them to check and make sure cookies are enabled on there browser. And they both said that it was.

I also told them to purge there cache and everything too. But it is still not working. They both also said the widget on the side of my site is not updating either.

Like I said before it works for myself flawlessly but I would like to see if I can help them out better because I have a chance to get alot of money from them both from buying from my site.

Could I get a few people to test for me and see if this is happening to them as well? You don't have to buy anything. Just add a few products to the shopping cart and see if it goes though. and updates for you. I would like a few people to test it out and see for me if they might get the same problem and tell me on here if it worked for them or not.

Thank you. Also if some one might know why. Please enlighten me as well so I can tell them how to fix it.