The lidgren client cannot connect to the server (as SinglePlayerSession) in the following cases:
Ip address is set to IPAddress.Loopback, IPAddress.Any when in Airplane mode or no network adapters are connected.
I have not been able to replicate this on Windows 7 dev environment, but I have on one non-dev machine. The sockets seem to bind find to 0.0.0.0:port, but the client messages never reach the server thread.
Upon further testing, it seems the client will connect if all network adapters are "disabled", but if any are enabled but not connected/plugged in the client will fail to connected even when IP address is any or loopback.