This error will only occur if:
1.) You typed the URL format incorrect or used the wrong IP/PC name and port number.
2.) TNG is blocked by the firewall.
3.) TNG is blocked by the proxy.
Suggestion:
Check the TNG log file for errors, for example:
a) socket error 10013
Description: An attempt was made to access a socket in a way forbidden by its access permissions.
The TNG port is blocked(default port is 7080) . Please ask IT to unblock it.