IMAP BAD protocol error

[John Cooper <john.cooper@eu.citrix.com>]

I occasionally (typically 2-3 times a day) get an IMAP BAD protocol error,
after which my Emacs process hangs (C-g is ignored) and has to be killed.
Here's the info from the *imap-debug* buffer:

  1 -> imap-search: predicate="UNSEEN UNDELETED" buffer=nil
  | 2 -> imap-mailbox-put: propname=search value=dummy mailbox=nil buffer=nil
  | 2 <- imap-mailbox-put: t
  | 2 -> imap-send-command-wait: command="UID SEARCH UNSEEN UNDELETED" buffer=nil
  | | 3 -> imap-send-command: command="UID SEARCH UNSEEN UNDELETED" buffer=nil
  | | | 4 -> imap-send-command-1: cmdstr="859 UID SEARCH UNSEEN UNDELETED"
  | | | 4 <- imap-send-command-1: nil
  | | 3 <- imap-send-command: 859
  | | 3 -> imap-wait-for-tag: tag=859 buffer=nil
  | | | 4 -> imap-arrival-filter: proc=#<process imap> string="855 BAD Protocol Error: \"Invalid ASTRING for folder name in STATUS command\"
  "

I'm using Debian Linux (woody), Emacs 21.2.1 and Oort Gnus v0.08 from the
nightly CVS from 1st November 2002 and the IMAP server is MS Exchange:

  1 -> imap-capability: identifier=IMAP4rev1 buffer=" *nnimap* hwmail01"
  1 <- imap-capability: (IMAP4REV1 IDLE LITERAL+ LOGIN-REFERRALS MAILBOX-REFERRALS NAMESPACE AUTH=NTLM)


Has anyone else seen the above BAD Protocol error?  Any ideas what could cause
it and what I might try to fix or workaround it?

Thanks,

    --- John