Asp.net ile kodlanmış bir siteye, php cURL ile giriş yapmaya çalışıyorum ancak. Site

<!-- Web.Config Configuration File -->

<configuration>
<system.web>
<customErrors mode="RemoteOnly" defaultRedirect="mycustompage.htm"/>
</system.web>
</configuration>

Hatasını veriyor.
İsteği aşağıdaki gibi yapıyorum

$post_data = 'Email=axtx@xyz.com&Sifre=123456&guvenlik=1';
$curl = curl_init();curl_setopt($curl, CURLOPT_URL, "http://www.bursagb.com/giris.html");
curl_setopt($curl, CURLOPT_HEADER, 1);
curl_setopt($curl, CURLOPT_REFERER, "Googlebot/2.1 (+http://www.google.com/bot.html)" );
curl_setopt($curl, CURLOPT_USERAGENT, "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:11.0) Gecko/20100101 Firefox/11.0");
curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, FALSE);
curl_setopt($curl, CURLOPT_SSL_VERIFYHOST, 2);
curl_setopt($curl, CURLOPT_ENCODING, "");
curl_setopt($curl, CURLOPT_COOKIEJAR, "dosya.txt");
curl_setopt($curl, CURLOPT_COOKIEFILE, "dosya.txt");
curl_setopt($curl, CURLOPT_VERBOSE, 1);
curl_setopt($curl, CURLOPT_POST, true);
curl_setopt($curl, CURLOPT_POSTFIELDS, $post_data);
curl_setopt($curl, CURLOPT_FOLLOWLOCATION, true);
curl_setopt($curl, CURLOPT_RETURNTRANSFER, true); 
$veri = curl_exec($curl);
echo $veri;
curl_close($curl);

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