[SOLVED] Apex Legends Javelin Error [4] - Disable AdGuard for Windows

[SOLVED] Apex Legends – EA Javelin Anti-Cheat Error [4] – AdGuard for Windows Was the Cause

TL;DR – Here's What Fixed It

If you're getting EA Javelin Anti-Cheat Error [4] when trying to enter the Firing Range or a match, try turning off AdGuard for Windows.

I'm talking about the desktop application, NOT the browser extension.

My friend had this exact problem on the PC (Steam) version of Apex Legends. We spent around 5 hours trying to fix it, and nothing worked.

Then we disabled AdGuard.

AdGuard ON: Error [4], couldn't enter the Firing Range or matches.

AdGuard OFF: Everything worked normally.

Seriously, that was it. After 5 hours of troubleshooting, turning off AdGuard fixed the problem.

I'm posting this in case it saves someone else from going through the same thing.

1. What Was Happening?

My friend was playing Apex Legends on Windows PC through Steam.

The game itself launched just fine, and he could get into the main lobby without any issues.

But whenever he tried to enter the Firing Range or join a match, EA Javelin Anti-Cheat would throw Error [4].

We also ran into matchmaking problems, including "Party Not Ready."

Another weird thing was that Steam's file integrity verification kept finding 3 files that needed to be reacquired.

Steam would download those files again, but the error would come back when we tried playing.

Sometimes Steam would even say all the files were fine, but the game still wouldn't let him enter the Firing Range.

2. Things We Tried That Didn't Work

We searched through EA forums, Apex Legends discussions, and even communities for other games using EA Javelin Anti-Cheat.

We also tried troubleshooting suggestions from AI tools.

Over roughly 5 hours, we tried quite a few things.

Game Files and Installation

Verified Steam game files multiple times.

Redownloaded the same 3 files repeatedly.

Reinstalled Apex Legends.

Tried both Steam and the EA app.

Moved the game from an external SSD to an internal drive.

Physically disconnected the external SSD and reinstalled the game on the internal drive.

Restarted Windows.

Anti-Cheat and Windows Services

Checked the EA Javelin Anti-Cheat service.

Looked into possible service and permission issues.

Tried administrator privileges.

Checked Windows services such as DNS Client, Cryptographic Services, and BITS.

Other Software and Network Settings

Investigated possible conflicts involving Fasoo DRM, which is used by some e-book and document security applications.

Disabled Internet Protocol Version 6 (TCP/IPv6) in Windows network adapter properties.

Looked into VPN-related issues and network connection settings.

Checked whether other background applications might be interfering with the anti-cheat.

Unfortunately, none of these worked.

At this point, we were pretty much out of ideas.

3. What Finally Worked – AdGuard

While we were talking about VPNs and network-related software, my friend suddenly remembered that he had AdGuard installed on his PC.

We figured it was worth a shot, so he disabled it.

And somehow, that fixed everything.

The game could finally enter the Firing Range and matchmaking normally.

Again, this was AdGuard for Windows, the actual desktop application, not a browser extension.

We hadn't seen many people mentioning AdGuard as a possible cause, which is why it took us so long to figure out.

4. Why Would AdGuard Cause This?

We're not completely sure.

Unlike a regular browser ad blocker, AdGuard for Windows can filter network traffic at the system level, including DNS and HTTPS traffic.

Our guess is that something in AdGuard's filtering process was interfering with Apex Legends or EA Javelin's connection or authentication process.

This is just our theory, though. We haven't identified the exact technical cause.

All we know for certain is that disabling AdGuard solved the problem on my friend's PC.

Of course, Error [4] could have other causes, so this might not work for everyone.

5. Final Thoughts

We spent around 5 hours trying just about every solution we could find.

Game reinstalls, changing drives, checking Windows services, disabling IPv6, investigating DRM software... none of it helped.

And in the end, it was AdGuard.

So if Apex Legends launches normally but throws Javelin Error [4] when you try to enter a match, please check whether you're running AdGuard for Windows.

Try temporarily disabling it and see if that fixes the issue.

If it works, you can look into AdGuard's filtering settings or exclusions instead of keeping it disabled permanently.

If anyone else manages to fix the same problem this way, please leave a comment. It would be interesting to know whether this is affecting more people.

Hope this helps someone!

A small note: English isn't my first language, so I used ChatGPT to help organize and write this post in English. The troubleshooting, symptoms, and solution are all based on what my friend and I actually experienced. We spent about 5 hours figuring this out ourselves. I just wanted to share what worked for us so others wouldn't have to go through the same trouble.