Problem automating login through php + curl - quite possibly due to __VIEWSTATE

Question

Hello,

I am trying to automate the login process for the site: winpossible.com. The site is running on .NET and expects the VIEWSTATE variable to be appropriate set and that is what is most probably tripping up the login function? Any tips on what maybe going wrong? The code is attached. Thanks in advance.

<?php

$username=urlencode('<something>');
$password="<something>";
$cookie="<cookie_file>";

$viewstate="...";
$postdata="__EVENTARGUMENT=&__EVENTTARGET=&__VIEWSTATE=$viewstate&_ctl0%3AContentPlaceHolder1%3APassword=$password&_ctl0%3AContentPlaceHolder1%3AUserName=$username&_ctl0%3AContentPlaceHolder1%3AbtnLogin.x=0&_ctl0%3AContentPlaceHolder1%3AbtnLogin.y=0";

$ch = curl_init();

$headers = 'Connection: Keep-Alive';

// First go to the home-page
curl_setopt($ch, CURLOPT_URL,"http://www.winpossible.com/");
curl_setopt($ch, CURLOPT_COOKIESESSION, true);
curl_setopt($ch, CURLOPT_COOKIEJAR, $cookie);
curl_setopt($ch, CURLOPT_COOKIEFILE, $cookie);
curl_setopt($ch, CURLOPT_VERBOSE, 1);
curl_setopt($ch, CURLOPT_USERAGENT, "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.6) Gecko/20070725 Firefox/2.0.0.6");
curl_setopt($ch, CURLOPT_HEADER, TRUE);
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
$result0 = curl_exec ($ch);
echo "Hi there - results of hitting the home-page\n";
echo $result0;

// Now try the login
curl_setopt($ch, CURLOPT_URL,"http://www.winpossible.com/LoginCheck.aspx");
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, FALSE);
curl_setopt($ch, CURLOPT_USERAGENT, "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.8.1.6) Gecko/20070725 Firefox/2.0.0.6");
curl_setopt($ch, CURLOPT_TIMEOUT, 60);
curl_setopt($ch, CURLOPT_HEADER, TRUE);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_COOKIESESSION, true);
curl_setopt($ch, CURLOPT_COOKIEJAR, $cookie);
curl_setopt($ch, CURLOPT_COOKIEFILE, $cookie);
curl_setopt($ch, CURLOPT_VERBOSE, 1);
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
curl_setopt($ch, CURLOPT_HTTPAUTH, CURLAUTH_ANY);
curl_setopt($ch, CURLOPT_REFERER, 'http://www.winpossible.com/Login.aspx');
curl_setopt($ch, CURLOPT_POSTFIELDS, $postdata);
curl_setopt($ch, CURLOPT_POST, 1);

$result = curl_exec ($ch);
echo $result;


// Now access my-account
curl_setopt($ch, CURLOPT_URL, "http://www.winpossible.com/");
$result2 = curl_exec ($ch);
echo $result2;

curl_close($ch);
// unlink($cookie);
exit;
?>