Magento – Displaying columns in Sales Order Grid

I have the following code to show some extra columns in the sales order grid. It correctly shows the columns and data, but when I try to click an order it says "No order exists".

I wondered if anyone can spot where I might be going wrong?

This code is in: /app/code/local/Mage/Adminhtml/Block/Sales/Order/Grid.php

class Mage_Adminhtml_Block_Sales_Order_Grid extends Mage_Adminhtml_Block_Widget_Grid
{

    public function __construct()
    {
        parent::__construct();
        $this->setId('sales_order_grid');
        $this->setUseAjax(true);
        $this->setDefaultSort('created_at');
        $this->setDefaultDir('DESC');
        $this->setSaveParametersInSession(true);
    }

    /**
     * Retrieve collection class
     *
     * @return string
     */
    protected function _getCollectionClass()
    {
        return 'sales/order_grid_collection';
    }

    protected function _prepareCollection()
    {
        $collection = Mage::getResourceModel($this->_getCollectionClass());

        $collection->getSelect()->join(array('billing'=>'sales_flat_order_address'),'main_table.entity_id=billing.parent_id and billing.address_type="billing"',array('*'));

        $collection->getSelect()->join(array('shipping'=>'sales_flat_order_address'),'main_table.entity_id=shipping.parent_id and shipping.address_type="shipping"',array('shipping.company as  shipping_company'));



        $this->setCollection($collection);

        parent::_prepareCollection();
        return Mage_Adminhtml_Block_Widget_Grid::_prepareCollection();
    }

    protected function _prepareColumns()
    {

        $this->addColumn('real_order_id', array(
            'header'=> Mage::helper('sales')->__('Order #'),
            'width' => '80px',
            'type'  => 'text',
            'index' => 'increment_id',
        ));

        $this->addColumn('created_at', array(
            'header' => Mage::helper('sales')->__('Order Date'),
            'index' => 'created_at',
            'type' => 'datetime',
            'width' => '100px',
        ));

        $this->addColumn('billing_name', array(
            'header' => Mage::helper('sales')->__('Billing Name'),
            'index' => 'billing_name',
        ));

        $this->addColumn('company', array(
            'header' => Mage::helper('sales')->__('Billing Company'),
            'index' => 'company',
            'filter_index' => 'billing.company',
        ));

        $this->addColumn('shipping_name', array(
            'header' => Mage::helper('sales')->__('Shipping Name'),
            'index' => 'shipping_name',
        ));

        $this->addColumn('shipping_company', array(
            'header' => Mage::helper('sales')->__('Shipping Company'),
            'index' => 'shipping_company',
            'filter_index' => 'shipping.company',
        ));

        $this->addColumn('grand_total', array(
            'header' => Mage::helper('sales')->__('Grand Total'),
            'index' => 'grand_total',
            'type'  => 'currency',
            'currency' => 'order_currency_code',
        ));

        $this->addColumn('status', array(
            'header' => Mage::helper('sales')->__('Status'),
            'index' => 'status',
            'type'  => 'options',
            'width' => '70px',
            'options' => Mage::getSingleton('sales/order_config')->getStatuses(),
        ));

        if (Mage::getSingleton('admin/session')->isAllowed('sales/order/actions/view')) {
            $this->addColumn('action',
                array(
                    'header'    => Mage::helper('sales')->__('Action'),
                    'width'     => '50px',
                    'type'      => 'action',
                    'getter'     => 'getId',
                    'actions'   => array(
                        array(
                            'caption' => Mage::helper('sales')->__('View'),
                            'url'     => array('base'=>'*/sales_order/view'),
                            'field'   => 'order_id',
                            'data-column' => 'action',
                        )
                    ),
                    'filter'    => false,
                    'sortable'  => false,
                    'index'     => 'stores',
                    'is_system' => true,
                ));
        }
        //$this->addRssList('rss/order/new', Mage::helper('sales')->__('New Order RSS'));

        $this->addExportType('*/*/exportCsv', Mage::helper('sales')->__('CSV'));
        $this->addExportType('*/*/exportExcel', Mage::helper('sales')->__('Excel XML'));

        return parent::_prepareColumns();
    }

    protected function _prepareMassaction()
    {
        $this->setMassactionIdField('entity_id');
        $this->getMassactionBlock()->setFormFieldName('order_ids');
        $this->getMassactionBlock()->setUseSelectAll(false);

        if (Mage::getSingleton('admin/session')->isAllowed('sales/order/actions/cancel')) {
            $this->getMassactionBlock()->addItem('cancel_order', array(
                'label'=> Mage::helper('sales')->__('Cancel'),
                'url'  => $this->getUrl('*/sales_order/massCancel'),
            ));
        }

        if (Mage::getSingleton('admin/session')->isAllowed('sales/order/actions/hold')) {
            $this->getMassactionBlock()->addItem('hold_order', array(
                'label'=> Mage::helper('sales')->__('Hold'),
                'url'  => $this->getUrl('*/sales_order/massHold'),
            ));
        }

        if (Mage::getSingleton('admin/session')->isAllowed('sales/order/actions/unhold')) {
            $this->getMassactionBlock()->addItem('unhold_order', array(
                'label'=> Mage::helper('sales')->__('Unhold'),
                'url'  => $this->getUrl('*/sales_order/massUnhold'),
            ));
        }

        $this->getMassactionBlock()->addItem('pdfinvoices_order', array(
            'label'=> Mage::helper('sales')->__('Print Invoices'),
            'url'  => $this->getUrl('*/sales_order/pdfinvoices'),
        ));

        $this->getMassactionBlock()->addItem('pdfshipments_order', array(
            'label'=> Mage::helper('sales')->__('Print Packingslips'),
            'url'  => $this->getUrl('*/sales_order/pdfshipments'),
        ));

        $this->getMassactionBlock()->addItem('pdfcreditmemos_order', array(
            'label'=> Mage::helper('sales')->__('Print Credit Memos'),
            'url'  => $this->getUrl('*/sales_order/pdfcreditmemos'),
        ));

        $this->getMassactionBlock()->addItem('pdfdocs_order', array(
            'label'=> Mage::helper('sales')->__('Print All'),
            'url'  => $this->getUrl('*/sales_order/pdfdocs'),
        ));

        $this->getMassactionBlock()->addItem('print_shipping_label', array(
            'label'=> Mage::helper('sales')->__('Print Shipping Labels'),
            'url'  => $this->getUrl('*/sales_order_shipment/massPrintShippingLabel'),
        ));

        return $this;
    }

    public function getRowUrl($row)
    {
        if (Mage::getSingleton('admin/session')->isAllowed('sales/order/actions/view')) {
            return $this->getUrl('*/sales_order/view', array('order_id' => $row->getId()));
        }
        return false;
    }

    public function getGridUrl()
    {
        return $this->getUrl('*/*/grid', array('_current'=>true));
    }

}