The software might have errors because the official website is not loading anymore. If the website and the VoIP server are hosted on the same machine, then this could be the cause to the error. If you attempt to load the website, a message like
ERR_CONNECTION_TIMED_OUT will appear.
Secondly, if you have the software, re-install it and make sure the Firewall is configured to allow Internet connection for the dialer application.