app/code/community/Adyen/Payment/Helper/Data.php
public function getSession()
    {
        if (Mage::app()->getStore()->isAdmin()) {
            $session = Mage::getSingleton('adminhtml/session_quote');
        } else {
            $session = Mage::getSingleton('checkout/session');
        }

        return $session;
    }
public function getSession()
    {
        if (Mage::app()->getStore()->isAdmin()) {
            $session = Mage::getSingleton('adminhtml/session_quote');
        } else {
            $session = Mage::getSingleton('checkout/session');
        }

        return $session;
    }
public function getSession ( ) { if ( Mage :: app ( ) -> getStore ( ) -> isAdmin ( ) ) { $ session = Mage :: getSingleton ( 'adminhtml/session_quote' ) ; } else { $ session = Mage :: getSingleton ( 'checkout/session' ) ; } return $ session ; }
Defines if it need to use the admin session or checkout session

@return mixed
Defines if it need to use the admin session or checkout session