That indicates that there isn't an Internet, Firewall or Port problem and at the very least you could continue to enjoy Internet Radio by manually entering the URLs of a handful of favorite stations while still pursuing a fix. If the entered URL plays, you can add it to a Playlist by right-clicking (or Ctrl + click) in the display window and choose Add to Playlist.
Do you have the latest version of iTunes? The latest version is 11.1.5.x for both OSX 10.6 or later and Windows XP or later. This problem has come up now and then over several years across multiple versions and sometimes a re-installation or a version update, if needed, fixes the problem. You can also try and clear warnings from Edit > Preferences > Advanced tab > Reset Warnings.
Steve