PHP Generate RSS XML - Encoding Error

So I have a small PHP script that generates an xml feel for the rss feed of my blog. However, it throws up this error:

This page contains the following errors:

error on line 23 at column 14: Encoding error
Below is a rendering of the page up to the first error.

(seen here: http://aviatex14.co.uk/rss.xml)

Here's the code that generates it:

while ($line = mysql_fetch_array($result))
        {
            $return[] = $line;
            var_dump(date("Y-m-d H:i:s", $line['timestamp']));

        }

$now = date("D, d M Y H:i:s T");

$output = "<?xml version=\"1.0\" encoding=\"UTF-16\" ?>
            <rss version=\"2.0\">
                <channel>
                    <title></title>
                    <link></link>
                    <description></description>
                    <pubDate></pubDate>
                    <language>en-us</language>

                    <lastBuildDate>$now</lastBuildDate>
            ";

foreach ($return as $line)
{
    $output .= "<item><title>".htmlentities($line['title'])."</title>
                    <link>http://blog.aviatex14.co.uk/permalink.php?uid=".htmlentities($line['uid'])."</link>

<description>".htmlentities(strip_tags($line['entry']))."</description>

<pubDate>".$date = date("Y-m-d H:i:s T", $line['timestamp'])."</pubDate>



                </item>";
}
$output .= "</channel></rss>";
print "Content-Type: application/rss+xml";
echo $output;

$f = fopen("rss.xml", "w"); 
fwrite($f, $output); 
fclose($f); 
?>

Any help would be appreciated! :D