1, the book format is wrong, and ePub or PDF format is needed;
2. Clear the ibooks data or download it again. IBooks uses books published in ePub format. To add ePub files outside the iBookstore to iBooks, these files must not be protected by DRM and be synchronized with the device using iTunes 9.2 or later. IBooks supports the industry-leading ePub digital book file type. You can use iTunes to sync free ePub files to iBooks, or download ePub files from iBookstore. IBooks also supports synchronizing and viewing PDFs. At present, other digital book file types are not supported.