in your Emacs, you should probably exit that Emacs and start a new one
to fire up Gnus.
-Gnus does absolutely not work with anything older than Emacs 20.3 or
-XEmacs 20.0. You definitely need a relatively current Emacs.
+Gnus does absolutely not work with anything older than Emacs 21.1 or
+XEmacs 21.4. You definitely need a relatively current Emacs.
To compile the Gnus manual, you either need a pretty new Emacs, or a
pretty new version of the texinfo tools.