problems reading IMAP mail

[David Nash]

I am a long-time user of RMAIL in emacs.  Now I am having to move to 
IMAP (ANU having discontinued POP access), and have today learnt 
enough about gnus to see my mail therein; and am struggling to regain 
the functionality I had with RMAIL.

I have looked found two threads here which are right on one of my problems:

Re: gnus-get-new-news with IMAP doesn't
http://lists.gnu.org/archive/html/info-gnus-english/2005-03/msg00089.html

Re: How to get new mail without leaving Summary buffer? 
http://lists.gnu.org/archive/html/info-gnus-english/2005-03/msg00200.html

but the suggestions there don't work for me (partly because I am 
using emacs over ssh so I don't control what software is on the host).

When I try to get new mail from the IMAP server, using M-g say, I get the error
"Ephemeral groups can't be reselected"

The host uses Gnus v5.9.0 and
GNU Emacs 21.4.1 (sparc-sun-solaris2.9)

Has anyone been down this path or can point me out of this?!
David