@SirBeardAlot: I tried the three scrambled versions that you sent. Only one of them caused any problems on my test device. This was the whose title started with "Finna dolda ting".
Firstly, one thing that was mentioned, but I didn't explicitly ask, is what format are you using? I didn't have any problems with the books as epubs. It was when I changed to using the KoboTouchExtended driver that the problem arose. This transformed the books to kepub. And as I suspected early, triggered a problem with the ToC. But, not one I had seen before.
The three books are ePub 3. The have the ToC as both an NCX and NAV document. For ePub3, the device is using the NAV document to get the ToC.
When I looked at the NAV document, called "ncc.xhtml" in each book, there where three sections:
- The basic ToC for chapters. This matched the NCX.
- A page list.
- The landmarks.
They were in that order and the landmarks were the largest section. As a test, I deleted the landmarks section, and the book was able to be processed by the device. I tried another version with the landmarks, but, without the page list and it didn't work.
Looking at the NAV document, the calibre editor showed it as 153.4KB. When I removed the landmarks, it dropped to 20.4KB. My assumption is that it was the sheer size of the text in the landmarks section that is causing the problem. There were only about 70 entries, so it had to be that. Or there was an error in them.
Beyond that, I can't say much. I know very little about how the NAV document works and even less about the landmarks. I have seen them before but not really looked at them. One thing that does look strange is that each landmark has "epub:type" of either "annotation" or "sidebar". My vague understanding is that they should point to sections in the book, such as the frontmatter, the backmatter and the first page of "real" content. As such, I would expect less entries and for them to be smaller. I don't know if this makes them invalid or not.