Spread cannot have more than 10 pages - what does this mean?

[default53x9pxnwvocf]

Hello there, often when synchronising (book) files or even (right now) when writing text on a page which does not affect the rest of the document in terms of space, a window pops up stating "Spread cannot have more than 10 pages". Why? How do I solve this? Also, I noticed that when adding a page to a file (which I just did because of this message, after which the file synched at last), the new page/s go to the right of the last spread in the pages panel. Why? Boo hoo! I would much appreciate any help. 

[Willi Adelberger]

Spreads a several pages, side by side. Normaly they are 2.

In the page panel menu allow pages to shuffle.

[default53x9pxnwvocf]

Thank you