@Nagano
Can i ask you try a sp game with just the invisible animal fix please and tell me if you still get the same error. (No other mods)
I know Jaxs increased biome zombie spawn edits the same stuff, so just want to see if those 2 conflict.
EDIT: nope those 2 together are fine. I am getting no errors at all in my logs.
can you post the spawning.xml from my mod that you have here (simply drag the xml into the little box in your reply and it will upload as a file.
That doesnt look like the current version is all as I have added to it in my latest version.
(possibly delete all copies you have of the invisi animals in downloads and in game folders, re download latest version and try again also.