使用PHP的Google日历ACL规则

为什么返回此输出"错误：请求的URL返回错误：400"而不是发送请求

$headers=array（"Authorization：GoogleLogin auth=".$this->auth."，"GData版本：2.0"，"传输编码：分块"，"内容类型：application/atom+xml")；
    $xmlstr = "<entry xmlns='http://www.w3.org/2005/Atom' xmlns:gAcl='http://schemas.google.com/acl/2007'
                    xmlns:gd='http://schemas.google.com/g/2005'
                    gd:etag='W/'"DU4ERH47eCp7ImA9WxRVEkQ.'"'>
                    <category scheme='http://schemas.google.com/g/2005#kind'
                    term='http://schemas.google.com/acl/2007#accessRule'/>
                    <gAcl:scope type='user' value='$email_id'></gAcl:scope>
                    <gAcl:role value='http://schemas.google.com/gCal/2005#read'></gAcl:role>
                </entry>";
    $url = "http://www.google.com/calendar/feeds/$cal_id/acl/full/user%3A".urlencode($email_id)."";

    curl_setopt($this->curl, CURLOPT_URL, $url);
    curl_setopt($this->curl, CURLOPT_HTTPHEADER, $headers);
    curl_setopt($this->curl, CURLOPT_CUSTOMREQUEST, 'DELETE');
    curl_setopt($this->curl, CURLOPT_POSTFIELDS, $xmlstr);
    curl_setopt($this->curl, CURLOPT_FOLLOWLOCATION, 1);
    curl_setopt($this->curl, CURLOPT_AUTOREFERER, true);
    curl_setopt($this->curl, CURLINFO_HEADER_OUT, false);
    curl_setopt($this->curl, CURLOPT_VERBOSE, true);
    curl_setopt($this->curl, CURLOPT_FAILONERROR, true);
    curl_setopt($this->curl, CURLOPT_COOKIESESSION, true);
    curl_setopt($this->curl, CURLOPT_HEADER, 0);
    curl_setopt($this->curl, CURLOPT_UNRESTRICTED_AUTH, true);
    $response = curl_exec($this->curl);