title: Same ID error during magento order export
body: <p>I am having trouble running an order export from my magento store. I keep getting the following error:
  <code>Item (Mage_Sales_Model_Order) with the same id "524" already exist</code></p>
  
  <p>Research has told me this is due to some bad records in my database, but I cant find any info on what those might be. I have looked for conflicting order numbers but there don't seem to be any.</p>
  
  <p>Does anyone know what the cause of errors like this is and/or how to find/fix the DB errors that cause it?</p>