SQLSTATE[42S22]: Column not found: 1054 Unknown column 'main_table.sfo.customer_email' in 'where clause' [closed]-Collection of common programming errors

Help. I have been struggling with this error for a few days now and have yet to find an answer. I am trying to add a few columns to the orders grid in Magento 1.6.2 I followed the instructions from: [http://www.milessebesta.com/web-design/magento-customize-backend-order-grid-to-have-sku-e-mail-address-and-phone-number/][1]

Here is the error message:

SQLSTATE[42S22]: Column not found: 1054 Unknown column ‘main_table.sfo.customer_email’ in ‘where clause’

Here is my code:

protected function _getCollectionClass()
{
    return 'sales/order_collection';
}

protected function _prepareCollection()
{

    $collection->getSelect()->group('main_table.entity_id');

    $collection->getSelect()->joinLeft(array('sfo'=>'sales_flat_order'),'sfo.entity_id=main_table.entity_id',array('sfo.customer_email','sfo.weight','sfo.discount_description','sfo.increment_id','sfo.store_id','sfo.created_at','sfo.status','sfo.base_grand_total','sfo.grand_total'));

    $this->setCollection($collection);

    return parent::_prepareCollection();
}

protected function _prepareColumns()
{
    $this->addColumn('real_order_id', array(
    'header'=> Mage::helper('sales')->__('Order *'),
    'width' => '80px',
    'type' => 'text',
    'index' => 'increment_id',
    'filter_index' => 'sfo.increment_id',
    ));

    if (!Mage::app()->isSingleStoreMode()) {
    $this->addColumn('store_id', array(
    'header' => Mage::helper('sales')->__('Purchased From (Store)'),
    'index' => 'store_id',
    'type' => 'store',
    'store_view'=> true,
    'display_deleted' => false,
    'width' => '40px',
    ));
    }
            $this->addColumn('customer_email', array(
    'header' => Mage::helper('sales')->__('Customer Email'),
    'index' => 'customer_email',
    'type' => 'text',
    'filter_index' => 'sfo.customer_email',
    'width' => '50px',
    ));

    return parent::_prepareColumns();
}

Check your database to see the actual name of the column you’re referring to. As Mysql says in its error: the column you’re addressing doesn’t exist.