I just had this bug using the latest version of dwarf fortress.
I read this thread and checked to see if there were files missing, but the save has hundreds of files along with the world.dat, so I don't really know what's wrong.
If I could get some help on how to fix this, I would be delighted, since this is an almost twenty year old fortress that I have been playing for the better part of a year, and losing it would really suck.
I'm using genesis mod, and I also did some modding of my own to make dragons breedable, which worked and never gave any trouble, and recently gave them wings and the flier tags. My error folder has no entries related to this issue, and I do have a copy of the entire region folder from maybe a month ago.
I really appreciate any help.
EDIT: I think I solved it. The date used by the bug to spring has passed with no event. After trying a lot of things and failing, I remembered I had given wings to a creature. I modded them away to their original state, and the bug didn't manifest. I wouldn't have thought that was the cause of this bug, but, I'm a happy overseer now.