smtp's failure due to starttls

[parmenides]

Hi,

I configured gnus to be the client of gmail, and tried to send email over 
smtp.
The '~/.gnus' is as follows:

(setq gnus-select-method '(nntp "news.cn99.com"))
(setq user-full-name "Parmenides")
(setq user-mail-address "mobile.parmenides@gmail.com")

(add-to-list 'gnus-secondary-select-methods '(nnimap "gmail"
                                  (nnimap-address "imap.gmail.com")
                                  (nnimap-server-port 993)
                                  (nnimap-stream ssl)))

(load-library "starttls")
(setq message-send-mail-function 'smtpmail-send-it
      smtpmail-starttls-credentials '(("smtp.gmail.com" 587 nil nil))
      smtpmail-auth-credentials '(("smtp.gmail.com" 587 
"mobile.parmenides@gmail.com" passwd))
      smtpmail-default-smtp-server "smtp.gmail.com"
      smtpmail-smtp-server "smtp.gmail.com"
      smtpmail-smtp-service 587
      smtpmail-debug-info t
      smtpmail-local-domain "")

When sending email, smtpmail-send-it issue some messages like these:

Process SMTP deleted
220 mx.google.com ESMTP y5sm79445tia.17

EHLO XF.

250-mx.google.com at your service, [219.228.59.9]

250-SIZE 35651584

250-8BITMIME

250-STARTTLS

250-ENHANCEDSTATUSCODES

250 PIPELINING

MAIL FROM:<mobile.parmenides@gmail.com> SIZE=675

530 5.7.0 Must issue a STARTTLS command first. y5sm79445tia.17

QUIT

221 2.0.0 closing connection y5sm79445tia.17

I think starttls must make some trouble. According to the gnus' manual, when 
connecting through tls, starttls.el and starttls program must exist. What is 
so called 'starttls program'? Is it starttls.elc?

Any suggestions are appreciated.