XML Parsing Error: xml declaration not at start of external entity

im building my own trackback class for my personal blog.

when i try calling my trackback URL like this: http://localhost/my-blog/this-is-a-test-entry/trackback/  i get the following error:

XML Parsing Error: xml declaration not at start of external entity
Location: http://localhost/my-blog/this-is-a-test-entry/trackback/
Line Number 1, Column 2: <?xml version="1.0" encoding="UTF-8"?>
-^

when i look at the source code, i dont have any whitespaces.  i have checked every line of my code over and over again incase i missed one hiding...

i searched on the web and read that a 8-bit character can be inserted infront of the XML declaration tag but i dont know how it could have?

if i create another example like below it works fine...

<?php
function test()
{
      $xmlWrite = '';
      $xmlWrite .= "<?xml version=\"1.0\" encoding=\"utf-8\" ?>";
      $xmlWrite .= "<test>";
      $xmlWrite .= "<success>works fine...</success>";
      $xmlWrite .= "</test>";
      
      return $xmlWrite;
}

header("Content-type: text/xml");
echo test();
?>

please see my original code below.  I know most of this is PHP so ive included this question in the PHP zone too...

trackback.php - the page that is called when user requests http://domain.com/my-blog/some-blog-entry/trackback/ :
 
<?php
header("Content-type: text/xml");
 
$host = trim($_SERVER['HTTP_HOST']);
 
if(substr($host,0,4) == 'www.')
{	
	$host = substr($host,4);
}
 
$now = date('Y-m-d G:i:s');
$ip = trim($_SERVER['REMOTE_ADDR']);
$agent = trim($_SERVER['HTTP_USER_AGENT']);
$domain = 'http://www.'.trim($host).'/';
 
require_once('classes/class.trackback.php');
 
$trackback = new Trackback('','','UTF-8');
 
global $response, $comment;
 
$tb_id = trim($HTTP_GET_VARS['id']);
$tb_title = trim($HTTP_POST_VARS['title']);
$tb_blog_name = trim($HTTP_POST_VARS['blog_name']);
$tb_url = trim($HTTP_POST_VARS['url']);
$tb_content = substr($HTTP_POST_VARS['excerpt'],0,2000);
$permalink = $domain;
 
if($_SERVER['REQUEST_METHOD'] != 'POST')
{	
	$err_response = 'XML-RPC server accepts POST requests only.';
}
 
// do a few checks to see if trackback is spam or already in table etc etc
 
if($err_response)
{
	echo trim($trackback->recieve(false,$err_response));
}
else
{
	echo trim($trackback->recieve(true,''));
}
?>
 
class.trackback.php recieve function:
 
 function recieve($success = false, $err_response = "") 
 {
        if (!$success && empty($err_response))
		{
            $err_response = "An error occured while tring to log your trackback...";
        }
        
		$return = '<?xml version="1.0" encoding="utf-8"?>'."\n";
        $return .= '<response>'."\n";
        
		if ($success) 
		{
            $return .= '    <error>0</error>'."\n";
        } 
		else 
		{
            $return .= '    <error>1</error>'."\n";
            $return .= '    <message>'.$this->xml_safe($err_response).'</message>'."\n";
        }
		
        $return .= '</response>';
 
        return $return;
    }

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