On Mon, 2009-07-27 at 16:56 +0100, Keith Edmunds wrote:

ls -l /home/publicfolders/dovecot-shared

-rw-rw-r-- 1 publicfolders publicfolders 0 2009-07-27 15:01 /home/publicfolders/dovecot-shared

This file probably isn't in the right place. It needs to be in each maildir under the publicfolders/ directory (i.e. where the dovecot-uidlist files are also).