nnshimbun problem

[Bill]

I recently activated a few shimbun groups (I may have used shimbun in
the past, but it's at least been quite a while).  They worked for a
few days, and then, starting this Monday morning, they keep gnus from
starting.

Gnus seems to go through my mail and newsfeeds okay, judging by the
minibuffer contents.  It reads some of the shimbun groups okay, too,
including (I think) Heise, zeit-de, and some of the bbc groups, but,
when it tries to read one of the bbc groups, I get "Cannot find
message-id base" in the minibuffer, the Gnu is in the main window, and
gnus stops.  Googling that phrase turns up sites such as
http://emacs-w3m.namazu.org/ml/msg06750.html, which seems to confirm
that it's a shimbun problem.

I suspect something changed at the bbc, or something got corrupted on
my system.  I thought it would be easy to start Gnus without reading
the shimbuns and then unsubscribing from the offending group, but I
can't get gnus to start without reading them.  I set gnus-activate-
level to 3 temporarily, because I was sure I had set all the shimbun
groups to level 4, but it still fails.  I tried gnus-no-server, but it
reads the offending bbc group anyway, so I must have missed setting
the level on it.

Is there a way to unsubscribe from those groups outside of Gnus?  Is
there a way to start Gnus successfully so I can read my mail and try
to fix the problem inside Gnus?

I'm running Gnus v5.11 and GNU Emacs 22.2.1 (as modified by Ubuntu).