If you try to use a nick that belongs to someone else who has protection on their nick, or that user uses the recover command on you: "When you give this command, NickServ will bring a fake user online with the same nickname as the user you're trying to recover your nick from. This causes the IRC servers to disconnect the other user." That is from this novernet
web page When you have a network specific question, its always best to go look at their website for info.