Magento Fatal Error in /IndexController.php on line 23

Question

I have a catalogue request page which is returning the following error when accessed: The page loads a blank page.

PHP Fatal error: require_once(): Failed opening required 'Mage/Core/Controller/Front/Action.php' (include_path='/var/www/includes/src:.:/usr/share/pear:/usr/share/php') in /var/www/app/code/community/Sqli/PaperCatalogRequest/controllers/IndexController.php on line 23

Line 23: inside IndexController.php is:

require_once('Mage/Core/Controller/Front/Action.php');

The file does exist on the server?

/var/www/app/code/core/Mage/Core/Controller/Front/Action.php

Action.php:

class Mage_Core_Controller_Front_Action extends Mage_Core_Controller_Varien_Action
{
    /**
     * Currently used area
     *
     * @var string
     */
    protected $_currentArea = 'frontend';

    /**
     * Namespace for session.
     *
     * @var string
     */
    protected $_sessionNamespace = 'frontend';

    /**
     * Predispatch: shoud set layout area
     *
     * @return Mage_Core_Controller_Front_Action
     */
    public function preDispatch()
    {
        $this->getLayout()->setArea($this->_currentArea);

        parent::preDispatch();
        return $this;
    }

    /**
     * Postdispatch: should set last visited url
     *
     * @return Mage_Core_Controller_Front_Action
     */
    public function postDispatch()
    {
        parent::postDispatch();
        if (!$this->getFlag('', self::FLAG_NO_START_SESSION )) {
            Mage::getSingleton('core/session')->setLastUrl(Mage::getUrl('*/*/*', array('_current'=>true)));
        }
        return $this;
    }

    /**
     * Translate a phrase
     *
     * @return string
     */
    public function __()
    {
        $args = func_get_args();
        $expr = new Mage_Core_Model_Translate_Expr(array_shift($args), $this->_getRealModuleName());
        array_unshift($args, $expr);
        return Mage::app()->getTranslator()->translate($args);
    }
}

This seems to have happened ever since the PATCH_SUPEE-5994_CE_1.5.0.1_v1-2015-05-15-04-34-32.sh was applied.

Running Magento version: Magento ver. 1.5.1.0

If anyone could advise of a solution, that would be a great help.