Problem with extension

<?php


if ( ! defined('EXT'))
{
  exit('Invalid file request');
}

class rsync_automation {

    var $settings = array();
    var $name            = 'Rsync Automation';
    var $version         = '1.0.0';
    var $description     = 'Kick off Rsync Automation Script';
    var $settings_exist  = 'n';
    var $docs_url        = '';
    

   function rsync_automation($settings='') {
      $this->settings = $settings;
   } //end constructor

    // --------------------------------
    //  Activate Extension
    // --------------------------------

    function activate_extension()
    {
        global $DB;

        $DB->query($DB->insert_string('exp_extensions',
            array(
                 'extension_id' => '',
                 'class'        => "rsync_automation",
                 'method'       => "build_rsync_tab",
                 'hook'         => "cp_display_page_navigation",
                 'settings'     => $this->settings,
                 'priority'     => 10,
                 'version'      => $this->version,
                 'enabled'      => "n")));
    }

    // --------------------------------
    //  Update Extension
    // --------------------------------

    function update_extension($current='')
    {
        global $DB;

        if ($current == '' OR $current == $this->version)
        {
            return FALSE;
        }

        if ($current < '1.0.1')
        {
            // Update to next version 1.0.1
        }

        if ($current < '1.0.2')
        {
            // Update to next version 1.0.2
        }

        $DB->query("UPDATE exp_extensions
                    SET version = '".$DB->escape_str($this->version).
                    "' WHERE class = 'rsync_automation'");
    }

    // --------------------------------
    //  Disable Extension
    // --------------------------------

    function disable_extension()
    {
        global $DB;
        $DB->query("DELETE FROM exp_extensions WHERE class = 'rsync_automation'");
    }


    /** -------------------------
    /**  Build Rsync Tab
    /** ------------------------- */
    function build_rsync_tab($this)
    {
           global $EXT,$SESS;
           if ($SESS->userdata['group_id'] == 1)  //super admin group
           {
                 if($EXT->last_call)
                 {
                    $EXT->last_call['rp'] = 'Rsync push';
                    return $EXT->last_call;
                 }
                 else
                 {
                    ;//$SESS->userdata['quicktabs']['rsync'] = 'Rsync Push|./index.php/?S=0&C=rsync';
                 }
          }
          return;
    }

} //end class