Using Disqus in a custom theme – problem

Firstly – this plugin is AWESOME. Many thanks!

I’ve added Disqus into my custom theme using a tutorial on WPTuts (http://wp.tutsplus.com/tutorials/plugins/integrating-disqus-into-wordpress/).

However, when I add this code into my functions.php file, the site runs fine, but when I try and log out of wp-admin, I get a blank screen.

This is the full content of my functions.php file:

<?php
function blog_filter($string, $show) {
    if ( $show == "description" ) {
        $string = str_replace('Text', '<a href="http://www.website.com/">Text</a>', $string);
    }
return $string;
}
add_filter('bloginfo', 'blog_filter', 10, 2 );
?>

<?php
function disqus_embed($disqus_shortname) {
    global $post;
    wp_enqueue_script('disqus_embed','http://'.$disqus_shortname.'.disqus.com/embed.js');
    echo '<div id="disqus_thread"></div>
    <script type="text/javascript">
        var disqus_shortname = "'.$disqus_shortname.'";
        var disqus_title = "'.$post->post_title.'";
        var disqus_url = "'.get_permalink($post->ID).'";
        var disqus_identifier = "'.$disqus_shortname.'-'.$post->ID.'";
    </script>';
}
?>

Can anyone please help? I’m so close!!

Thanks
John

http://wordpress.org/extend/plugins/disqus-comment-system/