Erro Com "simplexml_load_string()"

<?php

$data['token'] ='********************************';
$data['email'] = '*********@gmail.com';
$data['currency'] = 'BRL';
$data['itemId1'] = '1';
$data['itemQuantity1'] = '1';
$data['itemDescription1'] = 'teste';
$data['itemAmount1'] = '20.00';

$url = 'https://ws.pagseguro.uol.com.br/v2/checkout';

$data = http_build_query($data);

$curl = curl_init($url);

curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($curl, CURLOPT_POST, true);
curl_setopt($curl, CURLOPT_POSTFIELDS, $data);
curl_setopt($curl, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_1_1);

$xml = curl_exec($curl);

curl_close($curl);

$xml = simplexml_load_string($xml);//Linha: 38

echo $xml -> code;

	**ERRO:**

	**Warning**: simplexml_load_string() [function.simplexml-load-string]: Entity: line 1: parser error : Start tag expected, '<' not found in **C:\xampp\htdocs\sac\plugin\gateway\pagseguro\PagSeguro.php** on line **38****Warning**: simplexml_load_string() [function.simplexml-load-string]: Unauthorized in **C:\xampp\htdocs\sac\plugin\gateway\pagseguro\PagSeguro.php** on line **38****Warning**: simplexml_load_string() [function.simplexml-load-string]: ^ in **C:\xampp\htdocs\sac\plugin\gateway\pagseguro\PagSeguro.php** on line **38**