Php – Uncaught SoapFault exception: [WSDL] SOAP-ERROR [Magento][Ubuntu Server][Saop]

I have to use magento webservice to get data remotely from my server(ubuntu 10.04), so i have followed this tuto : http://magento4u.wordpress.com/2009/07/28/magento-api-web-service-work/,

but when I try to execute the method in code igniter Controller :

$proxy = new SoapClient('myhostname/soap/?wsdl');

$sessionId = $proxy->login('username', '***********');

$customerinfo = $proxy->customerCustomerInfo($sessionId,1);

print_r($customerinfo);

I get this error :

Fatal error: Uncaught SoapFault exception: [WSDL] SOAP-ERROR: Parsing
WSDL: Couldn't load from 'http://hostname.com/api/soap/?wsdl' :
Entity 'copy' not defined in
/var/www/happyprojects/api/application/controllers/users.php:42 Stack
trace: #0
/var/www/happyprojects/api/application/controllers/users.php(42):
SoapClient->SoapClient('myhostname', Array) #1 [internal function]:
Users->magento_call_get() #2
/var/www/happyprojects/api/system/core/CodeIgniter.php(359):
call_user_func_array(Array, Array) #3
/var/www/happyprojects/api/index.php(219):
require_once('/var/www/happyp…') #4 {main} thrown in
/var/www/happyprojects/api/application/controllers/users.php on line
42

Please can you help really I'm blocked, I don't know what to do.