Paradox decided to drop a surprise patch today. Unfortunately, this patch changes the game's UI, and as such will cause the current version of the Fan Fork to crash on startup. We can't release a comp patch now, because we're kind of in the middle of working on v0.3. However, you can fix this issue by simply rolling back your version of CK2 to Patch 2.8.2.1. (This should also work for any other mods that crash on startup when using Patch 2.8.3.)

INSTRUCTIONS (for Steam users):

Right click on "Crusader Kings 2" in your Steam Library's game list
Click on the "Properties" in the dropdown menu
Go to the "BETAS" tab of the window that pops up
Click on the beta list (where it says "NONE - Opt out of all beta programs")
Scroll to the bottom of the list and select "2.8.2.1 - Old Version 2.8.2.1"
Wait for Steam to roll back your install

If you keep having issues after this point, please manually download the mod from the Paradox Forums thread. It's linked in the mod's description.

i manually downloaded it and it still crashes on launch, only works when on 2.7.1 without fan fork

So I downloaded this on steam and a couple months ago it was working great. Just recently got out of basic and started trying to play again and it crashes before the start screen. I’m honestly not really sure what to say about it but if anyone has any ways to fix this that’d be great.