Google Base and Page Not Found problem

I submitted products to Google Merchant Center (Google Base) and Google needs to access the photos of the items I submitted to Google Base. All product photos are located at [domain url]/images/product/ directory. Although all the images exist in this directory, Google keeps getting “Page Not Found” instead of the actual image that is associated with the product.

I also get “Page Not Found” message when I try to access images directly. For example, [domain url]/images/product/image.jpg. Can anyone please help me how to fix this problem?

Thank you,