Trouble setting up Gnus + OfflineIMAP + dovecot

[Julien Cubizolles]

Following the examples provided on this list, I've setup Gnus to use a
maildir populated by OfflineIMAP as follows:

--8<---------------cut here---------------start------------->8---
(setq gnus-secondary-select-methods
      '(
        (nnimap "FreeOffline"
                (nnimap-stream shell)
                (nnimap-shell-program "/usr/lib/dovecot/imap -o 
mail_location=maildir:$HOME/Maildir-free")
                )
        (nnimap "GmailOffline"
                (nnimap-stream shell)
                (nnimap-shell-program "/usr/lib/dovecot/imap -o 
mail_location=maildir:$HOME/Maildir-gmail")
                )       
))
--8<---------------cut here---------------end--------------->8---

I've also some other nnimap backends (the ones actually synced by
OfflineIMAP until I make the final swith), some nntp.

I can Browse the GmailOffline server, which contains only one folder
named "INBOX" (I've only synced this one so far) but Gnus complains that
it cannot access it.

--8<---------------cut here---------------start------------->8---
Debugger entered--Lisp error: (error "Couldn’t enter nnimap+GmailOffline:INBOX")
  signal(error ("Couldn’t enter nnimap+GmailOffline:INBOX"))
  error("Couldn't enter %s" "nnimap+GmailOffline:INBOX")
  gnus-browse-read-group(no nil)
  gnus-browse-select-group(nil)
  funcall-interactively(gnus-browse-select-group nil)
  call-interactively(gnus-browse-select-group nil nil)
  command-execute(gnus-browse-select-group)
../--8<---------------cut here---------------end--------------->8---

Do you have any idea what I'm doing wrong ?