This happened after they did some upgrade to their servers. Kinoma cannot list books anymore either. Sent something to Audible Cust support and got this back. Still does not work though. Going to ping them back again:
On behalf of Audible I apologize for the inconvenience. With our recent updates there have been some issues that we are aware of and are working diligently to resolve. This also includes issues with Audible Air being down and is the reason you are receiving the error message you have. We are hopeful this will all be resolved very soon, try Audible Air tomorrow and everything should be back to normal, if not you can contact customer service or reply to this email for further assistance. In the meantime you will be able to download the title to your computer and transfer to your device. Feel free to contact us with any questions you may have.
For additional questions, how to contact us and hours of operation, please visit us at:
www.audible.com/contactus
Sincerely,
Audible Customer Support