The telnet server you are communicating with does not support the option to automatically transmit your user name.  Try having the server upgraded or leaving the “User Name” field empty in the Telnet Shortcut dialog.

That is not a properly formatted URL.

NiftyTelnet can not launch URLs until Internet Config is installed. 

Failed to open NiftyTelnet Prefs file.  Shortcut editing will be unavailable.

You must enter at least 4 for the window height.

You must enter at least 4 for the window width.

You must enter at least 150 for lines to keep for scrolling backwards.

You must enter a shortcut name.

Couldn’t save file “^0” due to a disk error.

The telnet server you are communicating with does not support the option to automatically recognize window resizing.  Consider upgrading the server software.

NiftyTelnet could not open “^0” because it only understands correctly formatted “telnet” URLs.

Not enough memory to open a new window. Try increasing the memory requirements for NiftyTelnet in the Finder’s get info dialog.