gnus imap error in 21.3

[Kin Cho]

Hi,

I use gnus via imap (over ssl) to get mail from our exchange
server as follows:

(setq nnimap-stream 'ssl
      gnus-select-method
      '(nnimap "mail-imap"
               (nnimap-address "ourexchsrvr")
               (nnimap-list-pattern "INBOX"))
       ;; ...
       )

All's well under 21.2.  However, under 21.3, this error traceback
happens when I select the "INBOX" group:

Debugger entered--Lisp error: (error "Couldn't open server")
  signal(error ("Couldn't open server"))
  error("Couldn't open server")
  gnus-select-newsgroup("INBOX" nil nil)
  gnus-summary-read-group-1("INBOX" nil nil nil nil nil)
  gnus-summary-read-group("INBOX" nil nil nil nil nil nil)
  gnus-group-read-group(nil)
  call-interactively(gnus-group-read-group)

I checked the version of gnus on both 21.2 and 21.3 is v5.9.0.

I'm running i386 RedHat 7.3.

-kin