title: Fatal error: Call to a member function toOptionArray() on a non-object in Magento admin
body: <p>When I click on Shipping Methods tab under Magento system->configuration->SALES tab I am faced with the following error:</p>
  
  <blockquote>
    <p>Fatal error: Call to a member function toOptionArray() on a non-object in D:\xampp\htdocs\magento\app\code\core\Mage\Adminhtml\Block\System\Config\Form.php on line 463</p>
  </blockquote>
  
  <p>The most astounding thing is that this is a fresh installation of Magento. Can anyone tell me how can I remove this error?</p>