加载xml文件时出错？

Question

动态加载xml文件并向api发送请求但是获取 Warning: DOMDocument::loadXML(): Empty string supplied as input in /home/spotrech/public_html/但是这个错误非常不一致有时会出现在某个时候！我真的不知道如何解决这个问题。下面是代码

$rechargeApiUrl = "http://allrechargeapi.com/apirecharge.ashx?uid=$uid&apikey=$apike&number=$mobileNo&opcode=$opId&amount=$amount&ukey=$uniId&format=xml";
$url = file_get_contents($rechargeApiUrl);
$xmlDoc = new DOMDocument();
$xmlDoc->loadXML(preg_replace('/(<\?xml[^?]+?)utf-16/i', '$1utf-8', $url));
$itemInfo = $xmlDoc->getElementsByTagName('Result'); //returns an object.
$itemCount = $itemInfo->length;
foreach ($itemInfo as $userInfo) {
    //Assigning node values to its specified  variables.
    $ukey = strtolower($userInfo->getElementsByTagName('ukey')->item(0)->childNodes->item(0)->nodeValue);
    $status = $userInfo->getElementsByTagName('status')->item(0)->childNodes->item(0)->nodeValue;
    $resultCode = $userInfo->getElementsByTagName('resultcode')->item(0)->childNodes->item(0)->nodeValue;
}

$strStatus = strtolower(trim($status));
$strResultCode = trim($resultCode);
$strCode = trim($ukey);

任何回复都将不胜感激。谢谢