Fatal error: Allowed memory size of 524288000 bytes exhausted (tried to allocate 37531648 bytes) 

<?php

class Company_Reports_Block_Adminhtml_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()->joinLeft('sales_flat_order_payment', 'sales_flat_order_payment.parent_id = main_table.entity_id',array('method'));
 

        // this is custom function that retrieves an array with payment option and its label
        $metode = $this->getActivePaymentMethods();

        // we get labels of payment options
        foreach ($collection as $afn) {
            foreach ($metode as $method) {
                if ($method['value'] == $afn['method']) {
                    $afn->setData('method', $method['label']);
                }
            }
        }

        $this->setCollection($collection);
        return parent::_prepareCollection();
    }
        protected function _prepareColumns()
        {
                $this->addColumn("increment_id", array(
                "header" => Mage::helper("reports")->__("Order #"),
                "align" =>"right",
                "width" => "50px",
                "type" => "number",
                "index" => "increment_id",
                ));
                
                $this->addColumn("billing_name", array(
                "header" => Mage::helper("reports")->__("Billing Name"),
                "index" => "billing_name",
                ));
            $this->addColumn("method", array(
                "header" => Mage::helper("reports")->__("Payment Type"),
                "index" => "method",
            ));
                $this->addColumn("pseudo_account_or_cc_no", array(
                "header" => Mage::helper("reports")->__("Cc Last 4"),
                "index" => "pseudo_account_or_cc_no",
                ));
            $this->addColumn("ops_alias", array(
                "header" => Mage::helper("reports")->__("Alias"),
                "index" => "ops_alias",
            ));
            $this->addColumn("grand_total", array(
                "header" => Mage::helper("reports")->__("Total"),
                "index" => "grand_total",
            ));
            $this->addColumn("total_paid", array(
                "header" => Mage::helper("reports")->__("Total Paid"),
                "index" => "total_paid",
            ));
            $this->addColumn('created_at', array(
                'header' => Mage::helper('sales')->__('Purchased On'),
                'index' => 'created_at',
                'type' => 'datetime',
                'width' => '100px',
            ));
                $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'=>'adminhtml/sales_order/view'),
                        'field'   => 'order_id'
                            )
                        ),
                        'filter'    => false,
                        'sortable'  => false,
                        'index'     => 'stores',
                        'is_system' => true,
                    ));
            }
                        
            $this->addExportType('*/*/exportCsv', Mage::helper('sales')->__('CSV')); 
            $this->addExportType('*/*/exportExcel', Mage::helper('sales')->__('Excel'));

                return parent::_prepareColumns();
        }

}

Fatal error: Allowed memory size of 524288000 bytes exhausted (tried to allocate 37531648 bytes)

<?php

class Company_Reports_Block_Adminhtml_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()->joinLeft(
            'sales_flat_order_payment',
            'sales_flat_order_payment.parent_id = main_table.entity_id',
            array('method')
        );

        // this is custom function that retrieves an array
        // with payment option and its label
        $metode = $this->getActivePaymentMethods();

        // we get labels of payment options
        foreach ($collection as $afn) {
            foreach ($metode as $method) {
                if ($method['value'] == $afn['method']) {
                    $afn->setData('method', $method['label']);
                }
            }
        }

        $this->setCollection($collection);
        return parent::_prepareCollection();
    }

    protected function _prepareColumns()
    {
        $this->addColumn('increment_id', array(
            'header' => Mage::helper('reports')->__('Order #'),
            'align' =>'right',
            'width' => '50px',
            'type' => 'number',
            'index' => 'increment_id',
        ));

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

        $this->addColumn('method', array(
            'header' => Mage::helper('reports')->__('Payment Type'),
            'index' => 'method',
        ));

        $this->addColumn('pseudo_account_or_cc_no', array(
            'header' => Mage::helper('reports')->__('Cc Last 4'),
            'index' => 'pseudo_account_or_cc_no',
        ));

        $this->addColumn('ops_alias', array(
            'header' => Mage::helper('reports')->__('Alias'),
            'index' => 'ops_alias',
        ));

        $this->addColumn('grand_total', array(
            'header' => Mage::helper('reports')->__('Total'),
            'index' => 'grand_total',
        ));

        $this->addColumn('total_paid', array(
            'header' => Mage::helper('reports')->__('Total Paid'),
            'index' => 'total_paid',
        ));

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

        $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'=>'adminhtml/sales_order/view'),
                        'field'   => 'order_id'
                    )
                ),
                'filter'    => false,
                'sortable'  => false,
                'index'     => 'stores',
                'is_system' => true,
            ));
        }

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

        return parent::_prepareColumns();
    }
}