Thanks for the quick re-sending of turns everyone. We are just waiting on Phonics/Atlantis now for the game to host.
Had a think about the whole hosting error, and because this type of error is AFAIK, almost exclusively linked to stealth units (hence the advice I was given suggesting to move scouts around to fix it), I have this funny feeling that the problem could be at Niefelheim's end and due to their Skratti unit.
Since depending on the orders and scripts, it is possible for a Skratti to be in a non-stealthed form when you press 'End Turn', yet still be hidden in enemy lands. I know this from previous testing, and from closer inspection of one of the turn 85's that came through to me when trying to locate the source of the error last night. As my patrols found a Skratti Werewolf hiding in one of my provinces, but the Skratti Werewolf isn't a stealth unit, so it shouldn't have been able to hide at all (at least not in that form). And I'm guessing there is a good chance the game engine doesn't like this sort of conflict, and is crashing during hosting as a result.
But guess we'll see what happens with the next attempted hosting, and take things from there if it fails again. I'm going away for a few days due to work commitments at the start of next week, so really hope this can be solved before then, and without the game having to take a mass stale (although if that becomes the only way to get past this error, then I guess it will have to be accepted
)