Received "Pong" : results in no connection

We have successful networking games working fine and dandy, but sometimes when we try to connect we get a mysterious message in the console (as shown above) from the server. The client then gets a NetworkConnectionError.ConnectionFailed error and obviously can’t connect. Usually if we restart the host once or twice this goes away. Any ideas what it means and why it’s there?

We are having the same problem described above, except that the error still there forever for some servers (behind “hard” routed networks). I believe that if my server can receive a “pong” from a client (whatever pong means) the client CAN connect to my server. Why is it not happening?