I created a 200 page Ebook with audio and video and although it exported and opens fine on my computer, my client (who is a teacher) says no one with a PC can open it and only one person with a Mac could. Is the file to big? Or is there something else that would be preventing it from working?
How are they trying to open it?
I assume this is a fixed layout epub which is only supported by limited reader apps. On Mac or iOS that would be iBooks.
For Windows, I've found Readium for Chrome to be about the best.