Quote from Trancid
Seems both of your errors are probably the same. Anyhow, going to take a stab in the dark, since Kinniken is absent.
From what I could tell from the mod-files, there is only one division in that specific routine. The 0 itself comes from getting the length of the building blocks, or something like that, of the building that is currently in the construction queue.
Long version short: somewhere in the past, either your save or your data files probably got corrupted in a way. If it can be fixed, well, you will need to ask someone with a lot more knowledge on the subject, like Kinniken himself.
Little side-question: The worlds you are playing in, were they by any chance worlds that were created in MC1.2.3 or even before that? (If it is even from before that, then I'm betting that blaming the conversion to the anvil format is a good chance.)
Actually, the world was created yesterday, and I never used Millenaire before MC1.2.4.
So Anvil seems not to blame this time
I now moved to another village, where this problem doesn't occur, because I don't want to lose the world or start (again) all over.
Anyway, I saw this error is listed in the FAQ, but the only hint given there is to ask here
Thanks for your help, Trancid (again) :3