OK, thanks to more information from Andrew, I've figured out what the problem was. Although it's true that iTunes annoyingly adds that iTunesMetadata file to your original EPUB file when you copy the file to iTunes, that's not what's causing the invalidation. But if you use iTunes to add a cover to your EPUB, as described in this video by Terry White, and then upload that EPUB to iTunes Producer, that EPUB will not validate and thus will not be accepted into the iBookstore, because the cover image is not properly contained in the OPF file.
Instead, the cover should be included in the EPUB file either via Pages' "Use first page as book cover image" option, or via the instructions in my book.
First update: I've just been able to upload an EPUB to the iBookstore with the iTunesMetadata.plist file intact, so I'm not sure exactly what's going on. It's not in the iBookstore yet, but the iTunes Producer says it validates, despite the iTunes file. I'll let you know what happens. It looks like I may have jumped to conclusions that the iTunes Metadata file was the culprit in this story. (It does continue to bug me that iTunes changes my files without asking!)
One of the things that this issue brings up is how hard it is to test things in the iBookstore. First, you have to sign up (which requires a US Tax ID and
I got a note on my blog the other day from Andrew Brooks who is publishing an enhanced ebook to the iBookstore. He has used Apple's Pages software to create the EPUB and even included enhanced elements. But when he went to upload the EPUB file to the iBookstore, he got this error:
“An Apple requirement is that all the files in the ePub be listed in the OPF file. So, the error was that there was an unmanifested iTunes artwork file.”
Little did he know that when he opened the EPUB file in iTunes, iTunes had the audacity to add a little file to his original EPUB document. No, not only to the EPUB that he copied to iTunes, but also to his original EPUB file. The file is called "iTunesMetadata.plist". You won't see it unless you look inside an affected EPUB.
To add insult to injury, when Andrew tried to upload his EPUB to the iBookstore, his ebook was rejected
It turns out that Andrew used iTunes to add a cover to his book, as described in this video by Terry White (and how people have been doing for records for a long time). Unfortunately, although the EPUB and cover will work properly in a local iPad, Apple won't accept it because the EPUB no longer validates. You have to add a cover to your EPUB either with Pages' "Use first page as book cover image" option, or via the instructions in my book.