Hey, I'm getting the error in the title for all ucore mods right now. Just to be sure I made sure I wasn't using the "dev" version like some others' issues have, and I stripped down to just the U Core and still have the error. Full crash report below. I do have alot of other mods and can post the list if necessary. LMK if there's another mod you're certain causes conflict and I can remove it to test. Other thing to note! I was using useful backbacks , one of the 1.16.4 versions, and that was all working before updating to the U Core april 1st update.

I'm running 1.16.5
FML: 36.1

crash-2021-04-15_16.10.16-fml.txt

Please post the whole crashlog / debug.log as a file

Please post the whole crashlog / debug.log as a file

updated with file

Do you use curseforge as a download site?
Can you try it with this exact file: https://www.curseforge.com/minecraft/mc-mods/u-team-core/download/3257635

I do use curse forge though I may have downloaded the wrong file, and had older versions of the others. I went through step and by step with fresh updates and installs and everything is working! Thank you for your time and sorry for the false alarm