Thanks Eric - I've not changed anything in the code for admin/index.php so not sure why it was throwing this error. On the basis of what you said though, I've moved the Connections/localhost.php up to the top of the includes list on this page, but I still get an error.
I've zipped the connections/localhost.php page and the globals page together with the admin index.php page in the hope that it might be something basic and stupid that I've done here.