If you use the trading platform at your workplace, it may be the case you are connected to the internet via firewall or a proxy server.
In such case go to ‘Tools – Options – Server’ and check 'Enable proxy server' box.
The settings of proxy server may be copied from Internet Explorer ‘Service – Viewer Properties – Connections – LAN Settings’.
The platform allows to work with SOCKS4, SOCKS5, and HTTP proxy servers. If the problem persists, ask your network administrator to open the port 443 or set up the port mapping to access the server.