From what I know from others, it is the version number (version compatibility) but also the "fact that agricultural science packs are now part of the item prototype not the tool prototype"...whatever that means. BTW I am not a modder😅
Ah, that would be a problem. It means the "type" field of science pack went from "tool" to "item", which would cause... I think either script crashed on game load, or may cause things to be missed, I'm not sure. Unfortunately, this also means I can't update the mod for 2.1 without breaking 2.0 compatibility.
I can tweak the version number if it's giving you errors, but you can also do this yourself. If you navigate to %appdata%\Factorio\mods (just paste this in your file explorer), then open NoTimedSpoilage_1.0.1.zip and edit the info.json file. I can give you more precise instructions if you'd like. Won't fix the tool/item change, though.