There might be 2 things.

1. Clear cache and test
2.  Their solution is to remove/comment those lines:
   In app/code/core/Mage/Downloadable/etc/config.xml:

   <code>

   <sales_order_item_save_after>
       <observers>
           <downloadable_observer>
               <class>downloadable/observer</class>
               <method>saveDownloadableOrderItem</method>
           </downloadable_observer>
       </observers>
   </sales_order_item_save_after>

   </code>

    
    
   And in app/code/core/Mage/Rss/etc/config.xml:
   <code>

   <sales_order_item_save_after>
       <observers>
           <notifystock>
               <class>rss/observer</class>
               <method>salesOrderItemSaveAfterNotifyStock</method>
           </notifystock>
       </observers>
   </sales_order_item_save_after>
   <sales_order_item_save_after>
       <observers>
           <ordernew>
               <class>rss/observer</class>
               <method>salesOrderItemSaveAfterOrderNew</method>
           </ordernew>
       </observers>
   </sales_order_item_save_after>

   </code>

   Maybe you can check if you can go without them and give a try. Remember that at next upgrade those changes will probably be lost.