Excerpt from an article on the Kotobee Blog:

It has become quite unlikely to submit anything to Apple without getting rejected at the first few attempts. Even ebooks.

Apple. Rejections. A very unfortunate combination. While the most common reaction to those long-awaited rejections would be to flip your keyboard into the air and punch the screen into the back wall, we would not advise that. There is a massive audience behind those over-protected Apple stores, very willing to pay for good products they find. Also, back wall maintenance may be expensive. So take a deep breath. Once you’re calm, let’s resolve the submission issues.

To find out more; and how to solve the issues, click on the link or image( used on their site) below:

Why your EPUB is being rejected from Apple iBooks Store