vmb01,
So we are able to produce the console screen, which means the VMRC application is starting in the background.
Then we basically try to connect to the Console Proxy address as specified in the Public Addresses section of vCloud Director (System > Administration).
If we cannot resolve the hostname or communicate with the IP Address it would resolve to, then that's just a general failure to communicate.
If you are using 1 cell, try putting the IP address in the public addresses section instead of a hostname and ensure your desktop can access the IP on port 443. if IP works, then it's name resolution from your system.
If you are using more than one cell and or a load balancer, can you bypass the load balancer and point to the console proxy IP of only one cell? if we bypass and it works, it's either the load balancer causing problems or how the certificates were setup.