Problems with adding product to cart in IE (all versions)

Hello!

My client recently pointed out an issue with adding products to the shopping cart in IE.
When she adds random products, sometimes the spinning circle keeps ... well, spinning, and the product does not get added to the shopping cart.

I have tried replicating the issue on different browsers and all work fine other than the IE browsers (7,8,9).

Just in case this is of importance to the issue:
The website uses 2 different wholesale categories where the products are the same however they have a different name (ex: "cd-hommus" and "hommus"). I have two different product pages that each call a different wholesale category. For wholesale category 1, there is no issue. For wholesale category 2, the products are not adding to cart (link and login details available on request, as the wholesale area of the website is private)

I would love to find what is causing this and how this can be remedied!

Thank you for your time!

Cheers,
Nancy