Warning: extract() expects parameter 1 to be array

<?php
if (!defined('WEB_ROOT')) {
    exit;
}

// make sure a product id exists
if (isset($_GET['productId']) && $_GET['productId'] > 0) {
    $productId = $_GET['productId'];
} else {
    // redirect to index.php if product id is not present
    header('Location: index.php');
}

// get product info
$sql = "SELECT *
    FROM tbl_product pd, tbl_category cat
        WHERE pd.pd_id = $productId AND pd.cat_id = cat.cat_id";
$result = mysql_query($sql) or die('Cannot get product. ' . mysql_error());
$row  = mysql_fetch_assoc($result);
extract($row);

// get category list
$sql = "SELECT cat_id, cat_parent_id, cat_name
    FROM tbl_category
        ORDER BY cat_id";
$result = dbQuery($sql) or die('Cannot get Product. ' . mysql_error());

$categories = array();
while($row = dbFetchArray($result)) {
    list($id, $parentId, $name) = $row;
    
    if ($parentId == 0) {
        $categories[$id] = array('name' => $name, 'children' => array());
    } else {
        $categories[$parentId]['children'][] = array('id' => $id, 'name' => $name);    
    }
}    

//echo '<pre>'; print_r($categories); echo '</pre>'; exit;

// build combo box options
$list = '';
foreach ($categories as $key => $value) {
    $name   = $value['name'];
    $children = $value['children'];
    
    $list .= "<optgroup label=\"$name\">";
    
    foreach ($children as $child) {
        $list .= "<option value=\"{$child['id']}\"";
        
        if ($child['id'] == $cat_id) {
            $list .= " selected";
        }
        $list .= ">{$child['name']}</option>";
    }
    
    $list .= "</optgroup>";
}
?>
<form action="processProduct.php?action=modifyProduct&productId=<?php echo $productId; ?>" method="post" enctype="multipart/form-data" name="frmAddProduct" id="frmAddProduct">
<p align="center" class="formTitle">Modify Product</p>

<table width="100%" border="0" align="center" cellpadding="5" cellspacing="1" class="entryTable">
 <tr>
  <td width="150" class="label">Category</td>
  <td class="content"> <select name="cboCategory" id="cboCategory" class="box">
   <option value="" selected>-- Choose Category --</option>
<?php
    echo $list;
?>