problem while running gnus

[null7]

Hallo
When I try to run gnus it fails with the following message
Symbol's value as variable is void: message-valid-fqdn-regexp

Just before running gnus I do M-x toggle-debug-on-error, but it does not open 
debug backtrace at gnus run.

*Message* buffer tells:
Loading gnus-agent...
Loading executable...done
custom-initialize-reset: Symbol's value as variable is void: 
message-valid-fqdn-regexp


I'm running:
emacs-version's value is "21.3.1"
gnus-version's value is "Gnus v5.10.6"

I'm running the newest version of gnus. To make emacs run it I delete previous 
version of grus from `load-path'. then I set up new path:

Loading /root/emacs/.emacs.gnus.el (source)...
deleting gnus path from load-path...
deleting path: /usr/share/emacs/21.3/lisp/gnus from load-path ;;; old path is 
removed at emacs startup
Loading /root/emacs/.emacs.gnus.el (source)...done

Code that does this trick is the following:

(setq my-gnus-dir "/root/emacs-packages/gnus-5.10.6")
(message "deleting gnus path from load-path..." (buffer-name))
      (dolist (load-path-entry load-path)
        (if (string-match "gnus" load-path-entry)
            (progn
              (message "deleting path: %s from load-path" load-path-entry)
              (setq load-path (delete load-path-entry load-path)))))

      (setq load-path (cons (concat my-gnus-dir "/lisp") load-path))
      (require 'gnus-load)

      (require 'info)
      (setq Info-directory-list
            (cons (concat my-gnus-dir "/texi") Info-default-directory-list))
      


finally, 
load-path's value is 
("/root/emacs-packages/gnus-5.10.6/lisp" "/root/emacs-packages/vm-7.19" 
"/root/emacs-packages/bbdb-2.34/lisp" "/usr/share/emacs/21.3/site-lisp" 
"/usr/share/emacs/site-lisp" "/usr/share/emacs/site-lisp/Mule-UCS" 
"/usr/share/emacs/site-lisp/psgml" "/usr/share/emacs/site-lisp/site-start.d" 
"/usr/share/emacs/site-lisp/table" "/usr/share/emacs/21.3/leim" 
"/usr/share/emacs/21.3/lisp" "/usr/share/emacs/21.3/lisp/toolbar" 
"/usr/share/emacs/21.3/lisp/textmodes" "/usr/share/emacs/21.3/lisp/progmodes" 
"/usr/share/emacs/21.3/lisp/play" "/usr/share/emacs/21.3/lisp/obsolete" 
"/usr/share/emacs/21.3/lisp/net" "/usr/share/emacs/21.3/lisp/mail" 
"/usr/share/emacs/21.3/lisp/language" 
"/usr/share/emacs/21.3/lisp/international" "/usr/share/emacs/21.3/lisp/eshell" 
"/usr/share/emacs/21.3/lisp/emulation" "/usr/share/emacs/21.3/lisp/emacs-lisp" 
"/usr/share/emacs/21.3/lisp/calendar" "/usr/share/emacs/site-lisp/psgml")

Do You know what might be the reason of that ?
Greetings