It's possible that Public Talk Scheduler might be discontinued because I couldn't find anything about it. That could be the main cause why the software is not connecting to the server.
Additionally, configure the firewall in your operating system to allow outbound connections initiated by the Public Talk Server. If you know how to add the program to exclusion do it this way or turn off the firewall to see if this is the problem.
Also, check the contact options and get in touch with the developers to ask them about the status of the software and servers.