Q: [2 ErrorMessage = ERROR ITMS-3000: "Line 9 column 76: element "related_item" incomplete; missing required element "identifier" at XPath /package/book/metadata/related_content/related_item  (1102) Can anyone help me solve this....evrytime try to deliver th

Hi, I keep getting an error message when trying to deliver my iBooks author book for publishing....anyone know how to solve this. Thanks

MESSAGE  AS FOLLOWS

[2013-08-18 20:08:57 CEST] <main> DBG-X:   parameter ErrorMessage = ERROR ITMS-3000: "Line 9 column 76: element "related_item" incomplete; missing required element "identifier" at XPath /package/book/metadata/related_content/related_item

(1102)