I was revisiting the installation of the Async client these days, and stumbled into an error when installing the Async Client for a R3 CU9 and trying to Test connection to the Async Server.
The error I got in the Event Viewer (of course in the client you will get that standard 3 possible issues form) was: "Unable to communicate with server for upload. Please check username/password, server and database connections. Error Details: System.ServiceModel.Security.SecurityNegotiationException: Could not establish trust relationship for the SSL/TLS secure channel with authority 'name:port'. ---> System.Net.WebException: The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel. ---> System.Security.Authentication.AuthenticationException: The remote certificate is invalid according to the validation procedure.".
So basically the issue here is that the certificates I used are not properly generated, and the problem was that the Issued To was not the same as the host name. Once I regenerated them, the installation went flawless.
For generating proper certificates you can find my previous post http://axfaq.blogspot.ro/2015/09/generate-certificates-with-crl-for.html.