Keep meaning to document this one, so here it goes.
Adding a site in VMware vSphere Replication fails with the error: Cannot connect to the specified site, site might not be available on the network or the network configuration may not be correct.
This may happen if you change the default network port for the vCenter Servers from 80 to another port number.
To resolve this issue when you are not using the standard port 80 or port 443, specify the port number in vSphere Replication: Add Site dialog.
Hope this helps you out.
thanks for reading.