Failed to open IMAP server

[TSUCHIYA Masatoshi <tsuchiya@namazu.org>]

Hi,

I face a quite mysterious trouble and am seeking advices.

My using softwares are:

    emacs-version => "24.3.1"
    gnus-version => "Ma Gnus v0.12"

I have just simplified my configuration into:

    (setq gnus-select-method '(nnimap "imap.example.net"))

However, Gnus failed to open the IMAP server.  Its error message is:

    Unable to open server nnimap+imap.example.net due to: Wrong type
    argument: listp, #<process *nnimap*>

I used edebug to investigate the cause of this trouble, and found that
open-network-stream() is called wihtout `parameters' argument.

In order to confirm my observation, I evaluated the following code and
tried re-connection.

    (defadvice open-network-stream
      (around check-parameters activate compile)
      (unless parameters
        (error "Unrecognizable error!!!"))
      ad-do-it)

Gnus's error message changed into:

    Unable to open server nnimap+imap.example.net due to: Unrecognizable
    error!!!

I believe that this is an evidence of my observation.

However, nnimap-open-connection-1() calles open-network-stream() with
`parameters' argument, as you know.

I cannot understand my observation and cannot imagine its cause.
Any comments and suggestions?

-- 
TSUCHIYA Masatoshi