Even with debug on, it doesn't output any error that might help. The evident cause for spitting this error is that the script is trying to concatenate the paths from cyrus-mailbox argument and the path for the subfolders.
Although I have some knowledge of perl, I didn't waste time finding the broken chunk of code trying some repairs. I searched for a quick solution and I found out that all I got to do is to rename mailboxes, subscription and .seen file names from british^songwriter to british.songwriter. ]

my proposition:

change cyrus2dovecot the following:

add:

$rootdir=~s/\^/xxminixx/g; #
$boxpath=~s/\^/xxminixx/g;

before this line:

# Let $box hold the path relative to the root directory (or "INBOX").
$box =~ s/^$rootdir\/+//;

and add this after it:

$rootdir=~s/xxminixx/\^/g;
$boxpath=~s/xxminixx/\^/g;

Regards Omar

Aug 10 14:07:55 server named[18622]: zone localhost/IN/localhost_resolver: loaded serial 42

Is this the last line that's in /var/log/messages ? Try and start named using

/etc/init.d/named restart

and then see what's written in the logs :

tail -f /var/log/messages

but
/etc/init.d/named start
Starting named: [FAILED]

if you could help me it would be good.

thank you.