On both SSO machines run the following in elevated command prompt
netsh advfirewall set allp state off
Hit enter
Then try again - this time with the IP address of the primary SSO and check
Another thing - are both sites in the same network segment? Is there a firewall in between? Are you able to open a web browser and open the XML page of the primary SSO server from the secondary SSO machine both by FQDN and by IP address?
