Amazon Payment OC 2.1.0.2

Hi,

I've installed and setup Amazon Payment in OC 2.1.0.2
When trying to pay with Amazon I get an error on the page (index.php?route=payment/amazon_login_pay/address) where I should choose the delivery adresse stating the following:

"When processing your payment there was a problem for for this site. Please contact the vendor if you need help."

I'm using Amazon German Marketplace.

Any idea what I might have missed during the configuration?

Thanks for the help,
Chris