Ah, the problem was the logout button.
<?php include $_SERVER['DOCUMENT_ROOT'] . '/artgibney/includes/logout.inc.html.php'; ?>
which is actually a form,
<form action="" method="post">
<div>
<input type="hidden" name="action" value="logout">
<input type="hidden" name="goto" value="/artgibney/admin/">
<input type="submit" value="Log out">
</div>
</form>
I have moved this line and it is working now.
Thanks for your patience with me.
Shane
PS The html you posted is no problem.