RTC connection over WAN - NAV 2013

I have installed Nav 2013 server and Sql server on a one machine and I have installed the windows client on another machine. The two machines are on separate active directory domains.
I have also configured the security certificates as per Microsoft documentation.
My problem is that the client is not able to connect to the server.
error message “The program could not create a connection to the server”

Anyone who has an idea what the problem could be.