It is a saying for "You have been disconnected from the network". This means your internet (Wireless or Ethernet) was disconnected while you were on Club Penguin. It happens every so often with a Wireless network. If you're still unable to reach Club Penguin, then try fixing your wireless adapter or your modem. Unplugging the modem for a moment is a great way to let it cool down, and that sometimes helps.
Alternatively, it could mean that another computer has just logged your penguin onto the same server which you were on, so be wary if you have ever given out your password.