--EDIT-- I'm an idiot. I thought I updated the mod after I updated factorio, and it hadn't. Upon seeing the mod hadn't updated, I applied the update and the game loaded.

Receive the following error message when opening the game:
"Failed to load mods: PlutoniumBreeding/prototypes/items.lua:28: attempt to index global 'item_sounds' (a nil value)
stack traceback:
PlutoniumBreeding/prototypes/items.lua:28: in main chunk
[C]: in function 'require'
PlutoniumBreeding/data.lua:1: in main chunk"

This sounds like the expected API break that was fixed in mod version 1.2.1. Are you on the latest version of this mod?

See edit. I'm sorry about the false report.