php写XML文件编码异常，求解答

php写XML文件编码错误，求解答
我有一个video的表，数据结构如下：


我利用如下程序读取表中文件，生成XML文件：

include("conn.php");

include("crop.php");



$xmlFile = "123.xml";

$dom = new DomDocument('1.0','utf-8');

$dom->formatOutput=true;

$thumbnails = $dom->createElement("thumbnails"); 

mysql_select_db('hdm0910283_db', $lnk) or die ('Can\'t use hdm0910283_db : ' . mysql_error());

mysql_query("SET NAMES utf-8");    

$sql="select * from video";

$query=mysql_query($sql);

while ($row = mysql_fetch_array($query)) {

	//切割youku截图

	$imageurl="../workshow/images/".$row[imgname];

    cutphoto("$imageurl","$imageurl",200,113);

	$dom -> appendChild($thumbnails); 

    $thumbnail = $dom->createElement("thumbnail");

    $thumbnail->setAttribute('filename', $row[imgname]);

    $thumbnail->setAttribute('label', $row[title]);

    $thumbnail->setAttribute('url', $row[url]);

	$thumbnails -> appendChild($thumbnail);

}

$dom->save($xmlFile);

运行的时候提示如下错误：
arning: DOMElement::setAttribute() [domelement.setattribute]: string is not in UTF-8 in D:\AppServ\www\rj\control\xml_do.php on line 20

Warning: DOMDocument::save() [domdocument.save]: output conversion failed due to conv error, bytes 0xCA 0xD3 0xC6 0xB5 in D:\AppServ\www\rj\control\xml_do.php on line 24

我测试过表中数据插入和读出均无问题，请高手帮助解决。 XML

------解决方案--------------------
mysql_query("SET NAMES utf8");
utf-8是无效的