TYPO3 Core

Hi all,

when accessing page after migration of Typo3 from version 4 to 6.1.7 i received this error:

Fatal error: Cannot access protected property TYPO3\CMS\Core\Database\DatabaseConnection::$link in ..\typo3conf\ext\realurl\class.tx_realurl.php on line 167

In this file on this line is following piece of code:

/************************************ * * Translate parameters to a Speaking URL (t3lib_tstemplate::linkData)
*****************************/

/**
 * Creates an instance of this class
 *
 * return    void
     */
    function tx_realurl() {
        if (!t3lib_extMgm::isLoaded('dbal') && get_resource_type($GLOBALS['TYPO3_DB']->link) == 'mysql link') {
            $res = $GLOBALS['TYPO3_DB']->sql_query('SELECT @VERSION');
            $rec = $GLOBALS['TYPO3_DB']->sql_fetch_row($res);
            $GLOBALS['TYPO3_DB']->sql_free_result($res);
            $this->useMySQLExtendedSyntax = version_compare($rec[0], '4.1.0', '>');
        }
        $sysconf = unserialize($GLOBALS['TYPO3_CONF_VARS']['EXT']['extConf']['realurl']);
        $this->enableDevLog = $sysconf['enableDevLog'];
    }

/**
 * PHP5-style constructor
 *
 * @return    void
     */
    function __construct() {
        $this->tx_realurl();
    }

Can somebody help me?
Thanks in advance.
Jakub