Broken/Choose a Nickname Prompt
The Choose a Nickname Prompt appears when you try connecting to a server with an invalid or taken nickname, or when you use the /nick command with an invalid nick. The prompt will not tell you which server you are changing nicknames on or anything useful. It will only ask for a nick.
If you give it an invalid nick, it will show the prompt again. If you do not give a nickname, or press the close window button on the top-right corner of the prompt, the prompt will close, as if you did not send an invalid nick or cause the server connection to fail with another prompt showing up with the message irc.server.net: Closing link: (numbers@ircipN.mibbit.com) [Registration timeout] or irc.server.net: Closing link: (ip) (Connection Timed Out). You may also get these errors if you do not give a valid nickname quick enough.