`elmo-imap4-spec-mailbox' instead of `elmo-imap4-spec-folder'.
                (elmo-imap4-send-command (process-buffer process)
                                         process
                                         (format "select \"%s\"" 
-                                                (elmo-imap4-spec-folder
+                                                (elmo-imap4-spec-mailbox
                                                  spec)))
                (setq msgdb (elmo-msgdb-load (elmo-string folder)))
                (setq response (elmo-imap4-read-response 
                (progn
                  (setcar (cddr connection) nil)
                  (error "Select folder failed"))
-             (setcar (cddr connection) (elmo-imap4-spec-folder spec))))
+             (setcar (cddr connection) (elmo-imap4-spec-mailbox spec))))
          (if response msgdb)))
     (elmo-msgdb-load (elmo-string folder))))