Thanks! I'll fix this in the next version.
Keep in mind that if this was caused by an update to 2.1 (which it looks like it was from the nature of the error), do be warned that things will (very likely) rerandomize in the new version anyways, since I have been changing the algorithm significantly with the recent updates. I would recommend keeping a 2.0 install beside your 2.1 one if you want to continue that world (it's not that bad! You just download from the website and it just works), or starting a new world.
