Gnus fetch gmail,ERROR

[ada]

hello
 
i follow the instruction on  http://www.pvv.ntnu.no/~terjeros/wiki/GnusGmail
to config my gnus to fetch gmail.but encounted follow ERROR:

Mail source (pop :server pop.gmail.com :port 995 :user dazhiqian :password 
******** 
:connection ssl :leave t) error (Cannot open load file).  Continue? (y or n) 
                                ~~~~~~~~~~~~~~~~~~~~~~~~
                                        WHY?   WHAT'S MEAN?                     
                   
nnml: Reading incoming mail from file...
nnml: Reading incoming mail (no new mail)...done


MY GNUS DOTFILE IS:

;;Fetch Email
;; The following line is needed when using pop3.el from T-gnus (m17n.org).
(eval-after-load "mail-source" '(require 'pop3))


;; using GNUS to send mail
(setq message-send-mail-function 'smtpmail-send-it)
(setq send-mail-function 'smtpmail-send-it)

;; use 'one file per mail' back end
(setq gnus-secondary-select-methods '((nnml "")))

;; tell Gnus how to fetch mail
(setq mail-sources '((file :path "/var/mail/ada")
                     (pop  :server "pop.gmail.com"
                           :port 995
                           :user "dazhiqian"
                           :password "******"
                           :connection ssl
                           :leave t))) ; leave the mail on the server

(setq smtpmail-default-smtp-server "smtp.gmail.com")
(setq smtpmail-smtp-server "smtp.gmail.com")
(setq smtpmail-local-domain nil)
(setq smtpmail-debug-info t)
(setq smtpmail-auth-credentials '(("smtp.gmail.com" 587 "dazhiqian"
"******")))
(setq smtpmail-starttls-credentials '(("smtp.gmail.com" 587 nil nil)))
(setq smtpmail-smtp-service 587)