Unable to login with Apple ID in iBooks Author
The error message is misleading. The real issue is that you need a separate Apple ID to publish ebooks.
Here's what you should do:


Go to https://appleid.apple.com and create a new Apple ID. When
asked for an email address, don't re-use the one you entered for
your primary iTunes account. I made that mistake and my account
became inaccessible. I had to call Apple support to finally fix the
problem.
Download iTunes Producer. Install and start it. Log in using your newly created Apple ID to your iTC account.
Create a new project in iTunes Producer. Add the cover image, the screenshots, and your ebook. Set the price and finally submit the book.