Not able to enter my Amazon Access Keys in AmazonSimpleAdmin

I tried to register my Amazon Account in AmazonSimpleAdmin (which is a plugin for Wordpress to show Amazon Affiliates on my blog.

After entering my Amazon Access Key ID and my Secret Access Key I got following error: "Error: AWS.InvalidAccount: Your AccessKey Id is not registered for Product Advertising API. Please use the AccessKey Id obtained after registering at http://ift.tt/1JHB1oS Get help at http://ift.tt/1S44gfv"

I tried without success:
* deleting my two Amazon Access Keys and recreated a new one.
* I double-checked if I had typos in the keys.