Fetch rss issues…

I use the following code to spit out the most 10 most recent posts from a blog listed in the directory I run.

For some reason the code works in one theme, but not the current theme which I like better.

$rss = fetch_rss($url);
$url = get_post_meta($post->ID, “RSS URL”, true);
if (is_array($rss->items)) {
$items = array_slice($rss->items, 0, 10);
echo ‘

‘;
foreach ($items as $item)
{
$desc = htmlspecialchars(substr(strip_tags($item[‘description’]),0,300));
echo ‘
• ‘ . $item[‘title’] . ‘

‘;
}
echo ‘

‘;
} else { echo ‘<p>No feeds yet. Come back soon!</p>’; }

gives me the error:
Fatal error: Call to undefined function: fetch_rss() in /www.bestgreenblogs.com/wp-content/themes/just-lucid/single.php on line 69

It works in my other theme, but why would it not work in the current one I use?