[vtiger][Webservice] Database error while performing requested operation - php

Question

I use the Vtiger webservice with its different methods CRUD, login ... etc. I created a task via the Calendar module, it worked well, but when I want to delete it does not work.
If I'm not mistaken, I need to have the object's id (so Calendar) in order to delete it. So I do:
public static function getTaskUser($user)
{
$idUser = self::getUserAccountId('XXXX');
$vtiger = new VtigerWS();
$connect = $vtiger->getConnection();
if ($connect && $connect['success'] == true) {
$response = $vtiger->query("id", "Calendar", "parent_id = '$idUser' ORDER BY id");
if ($response['success'] == false) {
$result = $response['error'];
} else {
$result = array();
foreach ($response['result'] as $task) {
$result[] = $task['id'];
}
}
} else {
$result = $connect['error'];
}
$vtiger->logout();
return $result;
}
==> In this function, I first look for the user id in vtiger (the user who was assigned to the previously created task). It works well.
But when the query is running:
($ vtiger-> query ("id", "Calendar", "parent_id = '$ idBaz' ORDER BY id");)
I get an error:
"code" => "DATABASE_QUERY_ERROR"
"message" => "Database error while performing requested operation"
The connection is good, I tried a query SELECT * FROM Calendar it does not work either ... I do not see where the error can come from.