paging error with php example

Hello,

I try to use pagination on grid, but when I clic on next, data is not loaded, here is my code:

index.php:

var dsOption =
        {
            fields :[
                {name : 'id'  },
                {name : 'f_name'  },
                {name : 'f_surname'  },
                {name : 'f_birthdate'  },
                {name : 'f_address' },
                {name : 'f_phone' },
                {name : 'f_mail' },
                {name : 'f_type' },
                {name : 'f_minor' },
                {name : 'f_sending' }
            ],
            recordType : 'object'
        }

var colsOption =
                [
                    {id: 'id' , header: "ID" , width:60},
                    {id: 'f_name' , header: "Prénom" , width:80},
                    {id: 'f_surname' , header: "Nom" , width:80},
                    {id: 'f_birthdate' , header: "Date de naissance" , width:120},
                    {id: 'f_address' , header: "Adresse" , width :100},
                    {id: 'f_phone' , header: "N° de Téléphone" , width :100},
                    {id: 'f_mail' , header: "Email" , width:80},
                    {id: 'f_type' , header: "Sex" , width:80},
                    {id: 'f_minor' , header: "Mineur" , width:100},
                    {id: 'f_sending' , header: "Réception" , width:100}
                ];

var gridConfig =
        {
            id : "scnf_grid",
            skin : 'mac',
            loadURL : 'Controller.php',
            exportURL : 'export_php/sncfList.php?export=true',
            exportFileName : 'sncf_data_form',
			container : 'sncf_grid',
            replaceContainer : true,
            dataset : dsOption,
            columns : colsOption,
            toolbarPosition : 'bottom',
            toolbarContent : 'reload | xls | filter | print | nav',
            pageSize : 20,
            pageSizeList : [05,10,15,20,25,50],
            encoding : 'UTF-8',
			showGridMenu : false,
            allowCustomSkin : true,
            filterable : true
        };

var mygrid=new Sigma.Grid( gridConfig );
		//Sigma.Util.onLoad( Sigma.Grid.render(mygrid) );
		Sigma.Util.onLoad(function(){mygrid.render()});

</script>

controller.php :

<?php
include 'export_php/ConnectionManager.php';

header('Content-type:text/javascript;charset=UTF-8');

$json=json_decode(stripslashes($_POST["_gt_json"]));

$conManager = new ConManager();
$conManager->getConnection();

if($json->{'action'} == 'load')
{
  $sql = "SELECT * FROM t_form_sncf";
  $handle = mysql_query($sql);
		
  $retArray = array();
  while ($row = mysql_fetch_object($handle))
  {
    $retArray[] = $row;
  }
  $data = json_encode($retArray);
  $ret = "{data:" . $data .",\n";
  $ret .= "recordType : 'object'}";
  echo $ret;
}
else if($json->{'action'} == 'save')
{
  $sql = "";
  $params = array();
  $errors = "";

$deletedRecords = $json->{'deletedRecords'};
  foreach ($deletedRecords as $value)
  {
    $params[] = $value->id;
  }

$sql = "DELETE FROM t_form_sncf WHERE id IN (" . join(",", $params) . ")";
  if(mysql_query($sql)==FALSE)
  {
    $errors .= mysql_error();
  }

$sql = "";
  $updatedRecords = $json->{'updatedRecords'};
  foreach ($updatedRecords as $value)
  {
    $sql = "UPDATE `t_form_sncf` SET ".
      "`f_name`='".$value->f_name . "', ".
      "`f_surname`='".$value->f_surname . "', ".
      "`f_birthdate`='".$value->f_birthdate . "', ".
      "`f_address`=".$value->f_address . ", ".
      "`f_phone`=".$value->f_phone . ", ".
      "`f_mail`=".$value->f_mail . ", ".
      "`f_type`=".$value->f_type . ", ".
      "`f_minor`='".$value->f_minor . "' ".
      "`f_sending`='".$value->f_sending . "' ".
      "WHERE `id`=".$value->id;
      if(mysql_query($sql)==FALSE)
      {
        $errors .= mysql_error();
      }
  }

$sql = "";
  $insertedRecords = $json->{'insertedRecords'};
  foreach ($insertedRecords as $value)
  {
    $sql = "INSERT INTO t_form_sncf (`f_name`, `f_surname`, `f_birthdate`, `f_address`,`f_phone`, `f_mail`, `f_type`, `f_minor`, `f_sending`) VALUES ('".
      $value->f_name."', '".$value->f_surname."', '".$value->f_birthdate."', '".$value->f_address."', '".$value->f_phone."', '".$value->f_mail."', '".$value->f_type."',  '".$value->f_minor."',  '".$value->f_sending."')";
    if(mysql_query($sql)==FALSE)
    {
      $errors .= mysql_error();
    }
  }

$ret = "{success : true,exception:''}";
  echo $ret;
}
?>

Any idea ?

data is correctly loaded and exported in excel just nav don't work