[twitter-dev] Cannot authenticate on Friendships/Destroy method

[RTuosto]

I'm trying to use the destroy friendships API method but I'm running
into a problem.

$login = "login: " .$_POST['authid'] . ":" . $_POST['authpassword'];
$url2 = "http://twitter.com/friendships/destroy/"; . $id . ".xml";
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url2);
curl_setopt($ch, CURLOPT_USERPWD, $login);
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
$result2 = curl_exec($ch);
curl_close($ch);
$xml = simplexml_load_string($result2);
var_dump($xml);

var_dump($xml) returns:
object(SimpleXMLElement)#4 (2) { ["request"]=>  string(33) "/
friendships/destroy/40627723.xml" ["error"]=>  string(27) "Could not
authenticate you." }

I only get this error on this method, I've been able to add friends,
and check statuses etc using the other API calls.

Whats going on?