Cannot modify header information.

Nogen der kan se hvorfor jeg får:
Warning: Cannot modify header information - headers already sent by (output started at /inc.xml.foreningmarkers.php:1) in /inc.xml.foreningmarkers.php on line 2

Hele tiden? Jeg har prøvet at sikre mig at der ikke står noget før header, samt prøvet med ob_start();

<?php
header("Content-type: text/xml");
echo "<?xml version='1.0' encoding='ISO-8859-1'?>";

function parseToXML($htmlStr)
{
$xmlStr=str_replace('<','&lt;',$htmlStr);
$xmlStr=str_replace('>','&gt;',$xmlStr);
$xmlStr=str_replace('"','&quot;',$xmlStr);
$xmlStr=str_replace("'",'&#39;',$xmlStr);
$xmlStr=str_replace("&",'&amp;',$xmlStr);
return $xmlStr;
}

$connection=mysql_connect (localhost, 'av2009');
if (!$connection) {  die('Not connected : ' . mysql_error());}

// Set the active MySQL database

$db_selected = mysql_select_db('akvarieviden', $connection);
if (!$db_selected) {
  die ('Can\'t use db : ' . mysql_error());
}

// Select all the rows in the markers table


$query = "SELECT * FROM forening WHERE aktiv = 1";
$result = mysql_query($query);
if (!$result) { 
  die('Invalid query: ' . mysql_error());
}


// Start XML file, echo parent node
echo '<markers>';

// Iterate through the rows, printing XML nodes for each
while ($row = @mysql_fetch_assoc($result)){
  // ADD TO XML DOCUMENT NODE
  echo '<marker ';
  echo 'name="' . parseToXML($row['navn']) . '" ';
  echo 'teaser="' . parseToXML($row['teasertext']) . '" ';
  echo 'lat="' . $row['lat'] . '" ';
  echo 'lng="' . $row['lng'] . '" ';
  echo '/>';
}

// End XML file
echo '</markers>';

?>