Thanks for the feedback everyone. I will roll the game back and attempt a re-host in the next few minutes then.
Get those fingers crossed
Edit 1: Ok, it's rolled back ok. Force hosting now.....
Edit 2: No new turn file yet, but just had an email telling me about an error again. So looks like it was a fail.....
Edut 3. No good, the error repeated itself with another mass round of stales. So guess the only real option now is to roll back to turn 84, and then for everyone to completely do their turn 84's again
re-doing a MM intensive late-game turn is surely the stuff of Dominions nightmares.
Will roll back again to turn 84 in a few minutes, and send out instructions to everyone in case anyone is unsure what is happening.