Problem configuring external vCO server in vCAC

Hi,

I am trying to connect my external vCO server (5.5) in vCAC 6.1 using Administration->Server Configuration->Use an external Orchestrator server", but I am getting error "Cannot connect to the Orchestrator server".

I have enter correct FQDN/IP Address and port 8281 but still I am not able to figure out what is the problem.

I believe this should be a very common issue but I did not find it on the internet. How do I troubleshoot this problem?

Thanks & Regards

Sandeep