Amazon changed the way that you access their feed.
To be compliant you need to use a new key and you need to send it to them in a special way.
I am currently looking into this but the change could expose developers to transfer costs for images and access to their feed sometime in the future so each user really needs to get their own key now which requires a Credit Card and new signup to AWS...
Just a heads up
This is costing a lot of people problems and more then a few Amazon projects have died because of it.