XML error parsing SOAP payload

[fedepia]

hello, i'm using sugar 5.0.0d and I'm trying to integrate an application with sugar. My problem is when invoking get_entry_list web service, the following result is retrieved:

Array
(
[faultcode] => Client
[faultactor] =>
[faultstring] => error in msg parsing:
XML error parsing SOAP payload on line 15: Invalid character
[detail] =>
)

my code is the following:

 $query = ' (LCASE(contacts.first_name) = \'' . $firstname . '\' AND LCASE(contacts.last_name) = \'' . $lastname . '\') ';
$result = $client->call('get_entry_list', array($session_id, $module_name, $query, "", 0, array(), 0, 0));
 
echo "<pre>" . print_r($result, true) . "</pre>"; 
  

I don't know what is the problem, so I did a print_r over $client and the sql generated was:

Cookie: PHPSESSID=17298f8ad156c45cc3e5d0d8a007ba75;
17298f8ad156c45cc3e5d0d8a007ba75Contacts (LCASE(contacts.first_name) = 'john'
AND LCASE(contacts.last_name) = 'doe' )

can be the sql generated the problem? if that is the problem how can I fix it?

thanks you

cheers