jQuery Grid Plugin - jqGrid

The grid works. The + opens the subgrid correctly and displays the header row. The correct number of rows display in the subgrid but are empty despite the correct json being created as displayed in firebug.

Code snippet for grid:-

// Create the jqGrid instance
$grid = new jqGridRender($conn);
// Write the SQL Query
// We suppose that mytable exists in your database
$grid->SelectCommand = "select uid,lastname,firstname,phonehome,phonework,mobile from students ".$where;

// set the ouput format to json
$grid->dataType = 'json';
// Let the grid create the model
$grid->setColModel();
// Set the url from where we obtain the data
$grid->setUrl('students/getstudents.php');
// Set grid caption using the option caption
$grid->setGridOptions(array(
    "caption"=>"Students and their Courses",
    "rowNum"=>16,
    "sortname"=>"lastname",
    "rowList"=>array(16,30,50),
    "height"=>354,
    "width"=>900
    ));

$grid->addCol(array("name"=>"act"),"first");

// Change some property of the field(s)
$grid->setColProperty("uid", array("label"=>"ID", "width"=>20, "hidden"=>true));
$grid->setColProperty("act", array("label"=>"Actions", "width"=>90));
$grid->setColProperty("lastname", array("label"=>"Last Name", "width"=>200));
$grid->setColProperty("firstname", array("label"=>"First Name", "width"=>150));
$grid->setColProperty("phonehome", array("label"=>"Phone Home", "width"=>150));
$grid->setColProperty("phonework", array("label"=>"Phone Work", "width"=>150));
$grid->setColProperty("mobile", array("label"=>"Mobile", "width"=>150));

$grid->setSubGrid("students/getcourses.php",
        array('Course','Status','Year','Semester'),
        array(300,150,40,50),
        array('left','left','right','center'));

Code for subgid

require_once '../includes/jquery/jq-config.php';
// include the jqGrid Class
require_once "../includes/jquery/php/jqGrid.php";
// include the PDO driver class
require_once "../includes/jquery/php/jqGridPdo.php";
// Connection to the server
$conn = new PDO(DB_DSN,DB_USER,DB_PASSWORD);

// Get the needed parameters passed from the main grid
$rowid = jqGridUtils::Strip($_REQUEST["id"]);
if(!$rowid) die("Missed parameters");

// Create the jqGrid instance
$grid = new jqGrid($conn);
// Write the SQL Query
$grid->SubgridCommand = "select courses.course, studcourse.status, courses.year, courses.semester from studcourse, courses where studcourse.studentno =".$rowid." and studcourse.courseno = courses.uid";

// set the ouput format to json
$grid->dataType = 'json';
// Use the build in function for the simple subgrid
$grid->querySubGrid(array(&$rowid));
$conn = null; 

json returned by subgrid code

{"rows":[{"course":"CSBM ","status":"Query","year":"2009","semester":"A"},

{"course":"FSB ","status":"Query","year":"","semester":""}]}

Can someone please tell me why these records are not being displayed in the subgrid.