Fatal error:  Call to a member function getId() on boolean in /home/site/public_html/csv/getAllOrders.php on line 28

$orders = Mage::getModel('sales/order')->getCollection()
    ->addAttributeToSelect('*')
    ->addAttributeToFilter('status', array('eq' => Mage_Sales_Model_Order::STATE_COMPLETE));

    foreach ($orders as  $order) {

        foreach ($order->getAllItems() as $item) {

            echo $item->getName() ." - ";
            echo $item->getSku();

            $product = Mage::getModel('catalog/product')->loadByAttribute('sku',$item->getSku());

            if($product->getId()){
                echo implode(",", $product->getCategoryIds());
            }
            echo "<br>";
        }
        echo "<br>*********************<br>";


    }