crash-2023-12-02_16.11.30-server.txt
how can i fix it? thanks

It looks like this is this bug: Qelifern/IronFurnaces#185

Probably easiest way to fix is remove iron furnaces from the mod folder, load into the world, then close it and add the mod back. Your furnaces will still be there but any upgrades/contents of the furnace will be removed and the settings reset.