Apple iTunes Producer Error Message

[Tim Ransom]

Hi,

I'm hoping that someone with Calibre and iTunes ebook publishing experience can enlighten me. I've converted my book into an epub file using Calibre. Upon delivery to iTunes, I get this error message:
ERROR ITMS-9000: "required attributes missing" at Book (MZItmspBookPackage)
Any thoughts on how to surmount this challenge?

After a quick web search regarding this error message, I found this posting:
http://forums.macrumors.com/showthread.php?t=934429
- indicating that I cannot publish directly to iTunes without an independent publisher.
Knowing Apple's history, I find this hard to believe. Is this true?

Thanks in advance for any help.
Regards, Tim