Trying to connect to ASPX site using CURL?

I am trying to log into this url:

http://www.kalahari.com/marketplace/default.aspx

The two fields that are being submitted are labelled:

ctl00$ctl00$ucMarketPlaceSupportNavigation$txtMPTopSignInEmail
ctl00$ctl00$ucMarketPlaceSupportNavigation$txtMPTopSignInPasswordTextNormal

The code I've tried to use so far:

$username     = 'XXXXXXX';
$password     = 'XXXXXXX';

$loginUrl     = 'http://www.kalahari.com/marketplace/default.aspx';
$cookie  = 'cookies.txt';

$ch = curl_init();

curl_setopt($ch, CURLOPT_URL, $loginUrl );
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, TRUE );
curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE );
curl_setopt($ch, CURLOPT_COOKIEJAR , $cookie);
curl_setopt($ch, CURLOPT_COOKIEFILE, $cookie);
curl_setopt($ch, CURLOPT_HEADER, FALSE );
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true);
$ret = curl_exec($ch); //access login page

// Collecting all POST fields
$postfields = array();
$postfields['ctl00$ctl00$ucMarketPlaceSupportNavigation$txtMPTopSignInEmail'] = $username;
$postfields['ctl00$ctl00$ucMarketPlaceSupportNavigation$txtMPTopSignInPasswordTextNormal'] = $password;

curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, $postfields);
$ret = curl_exec($ch);//Get result after login page.

print $ret;

This however only takes me back to the original login page... not even with an error message.

I then had a look at what is getting posted, and I saw:

Request URL:http://www.kalahari.com/marketplace/default.aspx
Request Method:POST
Status Code:302 Found
Request Headersview source
Accept:text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Charset:ISO-8859-1,utf-8;q=0.7,*;q=0.3
Accept-Encoding:gzip,deflate,sdch
Accept-Language:en-US,en;q=0.8
Cache-Control:max-age=0
Connection:keep-alive
Content-Length:2596
Content-Type:application/x-www-form-urlencoded
Cookie:VISITORID=9840A7E31683480CB19A66FB8AA7