HELP: "Publication exceeds maximum allowable file count of 65534 at Book

Hello,

hope anybody can help us. We got following error message while delivering the book on iTunes Connect: "Publication exceeds maximum allowable file count of 65534 at Book" (as attached).

The IBA file is 2,4 GB, once exported in .ibooks it is 1.8 GB. I'm not sure it has something to do with the file size because we already published bigger size files so far.

The book is a math textbook which includes about 500 HTML5 widgets, I'm not sure if this can be an issue..

Please help

Thanks in advance

Ugo