Thanks Chris
The entirety of my theme’s functions.php
<?php
if ( function_exists('register_sidebar') )
register_sidebar(array(
'before_widget' => '<li>',
'after_widget' => '</li>',
'before_title' => '<div>',
'after_title' => '</div>',
));
if ( function_exists( 'add_theme_support' ) ) {
add_theme_support( 'post-thumbnails' );
}
?>
so no add_filter there. Must say I have never used filters before.