[chrispedersen]

Here are edi's comments from today:
Patched to 3.20? I presume the answer is yes.
What mods are enabled?
Do you have scouts or otehr stealth troops moving more than one province per turn while sneaking? Are any of them flying?

Make a backup save of the game and try fiddling around with the movement orders of sneaking and hiding units you have and then rehost. When it goes away (and it should), make note of what you did. It might be helpful in conjunction with the log.

I experienced the same problem with a v3.19 game during the beta test and it was caused by a black harpy moving three provinces one turn and hiding the next. When I made the harpy move again, the turn hosted fine. At the time I was running CBM Pretenders 1.3, BI 2.1 and Worthy Heroes 1.8.

This may be related to something with a mod going wrong during hosting or something to do with move order validation, but I don't know for certain.