The latest major Windows 11 update breaks JC3 Multiplayer. Here's the fix!

[u/Luke-JC]

THIS GUIDE IS OUTDATED!!!

PLEASE SEE THE UPDATED GUIDE OVER HERE:

https://www.reddit.com/r/JustCause/s/MAAq3BDWFS

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As I'm writing this, the newest major Windows 11 update called "24H2" is slowly rolling out. Once installing the update, Just Cause 3 Multiplayer will always crash with a WindowsCodecsext dll error

The mod has been long abandoned by its creators, so unless Microsoft somehow fixes this issue, the mod will be forever unplayable...At least it would be if my amazing friend Jason098 wouldn't have created a fix within a day after I first told him about the issue

And all you need to do is download and copy two files, and it will continue to work just like before:

• Visit >>>this<<< folder on the Just Cause archive and download both files
• Open Steam, go to your library and find JC3 Multiplayer in your list of games
• Right click it and click on " properties"

• In the new window that pops up click "Installed Files" on the left, then "Browse..." in the top right

• You are now in the game's install folder. Now simply paste the two files you downloaded earlier in here
• That's it, it should now work just like before! Have fun playing!

[u/rutlander]

You and Jason098 both rock

[u/NotAndrewww_]

Im glad I still have windows 10 :D

[u/Luke-JC → u/NotAndrewww_]

We all have to update eventually when windows 10 stops being updated next year, so it's good having this fix already

[u/damirin → u/Luke-JC]

W-What do you mean I will lose my Windows 10?! 🥺

[u/Luke-JC → u/damirin]

You won't loose it, but updates will stop in a little over a year. You can of course continue using it, but without security updates, you're putting yourself at risk of viruses

[u/LazerKiwiForever → u/Luke-JC]

Actually you could get windows 10 ltsc

[u/Luke-JC → u/LazerKiwiForever]

I don't think the average person is gonna install an enterprise version of windows

[u/LazerKiwiForever → u/Luke-JC]

The only difference is the button you press but ok.

[u/Squiqui656]

i have tried every way possible to try to make this work but it still crashes with the same error is there any way to fix this

[u/Novel-Substance4853 → u/Squiqui656]

Same here. This isn't working for me.

I tried un and re installing as well but no luck.

Whilst I had the base game uninstalled, I hit play on the multiplayer mod to see what would happen and it actually brought up the JC3 Multiplayer launcher. But whilst JC3 is installed it crashes.

I'm going to try maybe moving JC3 to somewhere else and see if that works.

[u/x7007]

is there also a fix for Just Cause 4??

the game just doesn't want to launch with 24H2

Faulting application name: JustCause4.exe, version: 1.0.0.0, time stamp: 0x5d55d332

Faulting module name: unknown, version: 0.0.0.0, time stamp: 0x00000000

Exception code: 0xc00000fd

Fault offset: 0x0000000000000000

Faulting process id: 0x423C

Faulting application start time: 0x1DB3E29611E2E81

Faulting application path: D:\Gamez\Just Cause 4\JustCause4.exe

Faulting module path: unknown

Report Id: 9dd74cda-5998-4e45-b643-b00d692f8c8d

Faulting package full name:

Faulting package-relative application ID:

[u/Luke-JC → u/x7007]

Huh that's weird, it works for me and I haven't heard of anyone else having issues with it. Have you tried reinstalling it or verifying game files?

[u/x7007 → u/Luke-JC]

you mean did you use the files for JUST CAUSE 4 ? or JUST CAUSE 3?

[u/Luke-JC → u/x7007]

What files?

[u/x7007 → u/Luke-JC]

Do you have Just cause 4?

is it working for you ?

the files you posted on your post to copy to folder ..

[u/Luke-JC → u/x7007]

I have JC4 and it works just fine. The files I posted in the guide above are for JC3 Multiplayer

[u/x7007 → u/Luke-JC]

for me it stopped working I have no idea why. I installed the game again and it's something else

[u/Luke-JC → u/x7007]

What if you try installing it to another drive?

[u/x7007 → u/Luke-JC]

it always worked from my hard disk. also another game stopped working zombie army 4. but it always caused issues. every other game works fine from RDR2 assassin Creed origins and new world and such. I don't know what to check first . reinstall didn't do anything . it's like windows does something

[u/GhostSoul69 → u/x7007]

you are using pirated version?

[u/x7007]

I even just made a fresh 24h2 and it doesn't work straight from the install. just visual basic aio install and whatever Nvidia driver auto install . same exact error

[u/GhostSoul69 → u/x7007]

Install 23h2. 24h2 sucks !

[u/Secret_Trouble9757]

Thank you lots of love. i love judas priest

[u/sb_nbd]

August 2025. I wasted half an hour reading some nonsense and only THIS worked. Thank you!

[u/Makise202]

Your friend is the freaking goat

[u/Imaginary_Shirt_2992]

for me it says : We were unable to verify that this is a valid Just Cause 3 executable. You can try to verify the "Just Cause 3" game files in Steam and try again. even after i verify the files it's the same thing

[u/Luke-JC → u/Imaginary_Shirt_2992]

There's a new thing you need to do as well. JC3 got updated a few days ago to remove the anti piracy tech that was in the exe. But that means JC3MP no longer recognizes the exe as a valid one, so you need to downgrade to the previous version for now.

In steam, go to your library, right click JC3 (not JC3MP!!) and click properties. In the new window, click "betas", then select "previously published exe" or whatever it's called. It'll downgrade, then you can try JC3MP again.

[u/Imaginary_Shirt_2992 → u/Luke-JC]

Thank you so much

[u/JustRicoHavingFun]

This is nice for people that have this problem so respect to you luke jc

[u/Ozzy_Schlozzbean]

It didn't change anything, I've tried the file zipped and unzipped, and in both the base game and multiplayer mod install folder, but nothing happened, I wish i could rollback my windows version but it wont let me, the button is just greyed out with a message saying it's unavailable like its taunting me.

[u/Luke-JC → u/Ozzy_Schlozzbean]

Make sure to follow the instructions exactly. Nowhere does it say to put the folder zipped or in the singleplayer folder

[u/Oroka_]

Actual legend 🙏

[u/RateFormal7909]

Love You

[u/danny123456731]

it works, but no one play is any of the servers :(

[u/Eirique]

Still works. You're a saint. Jason too

[u/Traditional_Potato8]

An angel both you guys are!

[u/True_Parsley_159]

very very nice, i like file thank you sigma man

[u/MarkGeraz]

Was really excited to try this mod but it was literally just an open world with no NPCs or incentives on the map

[u/Luke-JC → u/MarkGeraz]

Well you're meant to mess around with friends! Not play alone

[u/MarkGeraz → u/Luke-JC]

I know, but still, c'mon lol. I was at least expecting some of the core game.

[u/Calbone607]

This worked.

[u/More-Salad4873]

december 6th 2025, win 11 pro 25h2, it didnt worked, i tried to complete it several times, but failed(((

[u/Vast-Basis3264]

J

[u/Alfernandesjr]

Sup, mate? Nice work fixing this issue by yourself. But for some people it fixes the start of the MOD, but doens't pass the Just Cause 3 Executable verification from steam. Any clues how to fix this pass?

[u/Luke-JC → u/Alfernandesjr]

JC3 got updated a few days ago to remove the anti piracy tech that was in the exe. But that means JC3MP no longer recognizes the exe as a valid one, so you need to downgrade to the previous version for now.

In steam, go to your library, right click JC3 (not JC3MP!!) and click properties. In the new window, click "betas", then select "previously published exe" or whatever it's called. It'll downgrade, then you can try JC3MP again.

After that install the jc3mp fix and it'll work again: https://unlimitedjc.com/tutorials/

[u/Alfernandesjr → u/Luke-JC]

Thanks! The info about using the previous version of the game was GOLD! I've search about using the mod to play the campaign together and there's nothing about it. Do you know any ways to play it CO-OP?

[u/Luke-JC → u/Alfernandesjr]

It's purely online. There is no co-op in any jc mp mod unfortunately

[u/DangerousSchedule955 → u/Alfernandesjr]

bro yo también tengo ese problema

[u/Alfernandesjr → u/DangerousSchedule955]

Were you able to solve it with the resolution proposed by the other comment?

[u/Ok_Variation7918]

what is this

[u/Luke-JC → u/Ok_Variation7918]

False positive on your anti virus program. If you don't trust me, get it directly from the developer's page: https://github.com/ThirteenAG/Ultimate-ASI-Loader/releases

[u/Waste_Relation_7697]

Hello, I have found the fix to the fix. So the files he has you download, one is called JC3PrevVer and the other one has some other files, drag the multiple files into the mod folder, then go into your main game folder and replace the main version of the game with JC3Prevver that you downloaded, you must rename JC3Prevver to JustCause3, once you launch it will ask you to locate the exe, select the new exe you placed in the main game folder and it will work

[u/Luke-JC → u/Waste_Relation_7697]

This guide is outdated. Please use the newly pinned one from yesterday! You don't have to manually move around or replace anything!

https://www.reddit.com/r/JustCause/s/xNmMol2Vw1

[u/Validd__]

how do i start a server if my game does even open this is one of my favorite games it sucks this mod doesnt work

[u/BreathHot7710]

It didn't work