How to Fix “An Error Occurred in e4mc” in Minecraft

If you’re getting “An error occurred in e4mc” when opening your world to LAN, you’re not alone. This error is one of the most common issues with the e4mc mod, and it has several distinct causes — relay server outages, mod conflicts, Java version mismatches, and authentication failures. This guide walks through every fix in order, from the quickest checks to advanced workarounds.

e4mc (Easy 4 Minecraft) is a Fabric mod that lets you share a local Minecraft world over the internet via a public LAN link — no port forwarding required. It routes your connection through relay servers, so friends on different networks can join as if they were on your LAN.

When the relay connection fails for any reason, the game shows the generic message: “An error occurred in e4mc.”

What Causes e4mc Error?

Before you start fixing the issue, identify what’s causing the failure. These are the most common reasons:

• Relay server issues are the leading cause. e4mc depends on regional relay servers (primarily in North America and Europe). If a relay goes down or is overloaded, connections fail silently. The QUIC protocol used for relay handshakes is particularly sensitive to high latency and NAT configurations.
• Mod conflicts are the second most common cause. Performance mods like Sodium, Lithium, C2ME, and network-altering mods like NoChatReports are known to interfere with how e4mc establishes its relay connection.
• Java version mismatches can cause underlying network stack errors. e4mc requires Java 17 and behaves unpredictably on older versions.
• Authentication failures occur when using unofficial (cracked) clients. Without a valid Mojang/Microsoft session, the relay authentication step fails entirely.
• ISP or firewall blocks can prevent the QUIC protocol from working, especially on strict corporate or university networks.

Quick Reference Table

Fix “An Error Occurred in e4mc” in Minecraft

Step 1: Check Relay Server Status

Before changing anything on your end, verify that e4mc’s relay servers are actually running.

1. Visit status.e4mc.link.
2. If servers show degraded or offline status, the fix is simply waiting for them to recover.
3. If North American relays are struggling, try forcing the EU region (see Advanced Tips below).

Relay outages — especially on NA servers — account for the majority of reports. This should always be your first check.

Step 2: Run a Clean Mod Setup

Many players unknowingly run mods that conflict with e4mc’s network behavior. The fastest way to confirm a mod conflict is to test with the bare minimum:

1. Open your .minecraft/mods folder (or the equivalent in your launcher profile).
2. Temporarily move all mods out except:
   • e4mc (latest version for your Minecraft version)
   • Fabric Loader
   • Fabric API
3. Launch Minecraft and try opening to LAN again.

Known conflicting mods include Sodium, Lithium, C2ME, NoChatReports, EnhancedBlockEntities, and various chat-altering or anti-telemetry mods. If the clean setup works, add mods back one at a time to find the culprit.

Step 3: Update Java and Launcher Settings

• Install Java 17 from Adoptium or through your launcher’s built-in Java manager. Avoid Java 8, 11, or 21+ for e4mc unless you’ve confirmed compatibility.
• In your launcher’s JVM arguments, set reasonable memory allocation:

 -Xmx4G -Xms2G

• Temporarily disable your firewall or antivirus, particularly any rules blocking javaw.exe.
• If you’re on Wi-Fi, try switching to a wired connection or a mobile hotspot. This rules out ISP-level QUIC filtering.

Step 4: Check Your Logs

If the error persists, your logs will tell you exactly what’s failing.

1. Open .minecraft/logs/latest.log in any text editor.
2. Look for these specific error patterns:

Relay/QUIC failure:

[nioEventLoopGroup-2-1/INFO]: [CHAT] An error occurred in e4mc
java.lang.RuntimeException: null
at link.e4mc.QuiclimeSession.lambda$start$4(QuiclimeSession.java:328)

Authentication failure:

com.mojang.authlib.exceptions.InvalidCredentialsException: Status: 401

QUIC implementation error:

DefaultPromise.setFailure
QuicheQuicChannel

Each of these points to a different fix. A RuntimeException: null in QuiclimeSession usually means relay timeout. An InvalidCredentialsException means you need to use an official Mojang/Microsoft account.

3. If you’re reporting a bug, include your log file and mod list at e4mc’s GitHub Issues page.

Step 5: Use an Alternative If e4mc Keeps Failing

If you’ve gone through the steps above and nothing works — particularly during extended relay outages — these alternatives can host a multiplayer session without e4mc:

• Playit.gg — The easiest drop-in replacement. It creates a public tunnel to your Minecraft server or LAN world. Free tier works well for small groups. No technical setup required.
• Ngrok — A general-purpose tunnel tool. Free plan works but resets your public URL every two hours. Slightly more setup than Playit.gg.
• ZeroTier — Creates a virtual LAN between devices. Works reliably even through strict NAT or firewalls, but all players need to install the ZeroTier client.

Advanced Fixes and Configuration

Force a Specific Relay Region

If NA relays are overloaded or unstable, you can pin e4mc to use EU relays by editing the mod’s config file (typically at .minecraft/config/e4mc.toml or a similarly named file in your config folder):

relay.region = "eu"

EU relays tend to be more stable during peak hours, even for players outside Europe. The latency penalty is usually worth the reliability improvement.

Version Compatibility

Not all combinations of e4mc, Fabric API, and Minecraft work reliably together. Use only tested pairings:

Avoid using experimental or snapshot Fabric builds with e4mc unless they’ve been explicitly tested. Check the e4mc GitHub releases page for the latest compatibility notes.

Doing a Full Clean Reinstall

If e4mc has been updated, upgraded, or migrated from an older instance:

1. Delete your .minecraft/mods folder contents.
2. Delete any e4mc-related files in .minecraft/config/.
3. Do not copy config files from an older installation — they may carry corrupted settings or outdated relay addresses.
4. Reinstall from scratch: Fabric Loader → Fabric API → e4mc only.

This resolves issues caused by stale configuration that silently breaks relay setup.

Network-Level Workarounds

If your ISP, router, or institution is blocking QUIC traffic (common on school or corporate networks):

• Use a mobile hotspot as your primary network while hosting — this bypasses most ISP-level filtering.
• Route through Playit.gg or Ngrok, which use TCP/HTTP tunneling instead of QUIC.
• Use ZeroTier to create a VPN-like virtual LAN that bypasses NAT entirely.

What the Error Looks Like in Logs (Reference)

For developers or advanced users wanting to understand what’s happening internally:

Most reported errors originate in QuiclimeSession.java during the relay setup phase. The underlying causes include:

• Null handling failures during relay handshake
• Relay timeouts that aren’t caught gracefully, causing a null RuntimeException to bubble up
• Silent QUIC disconnects that the client doesn’t recover from

Suggested improvements the community has proposed (and which may be addressed in future releases) include automatic retry across relay regions, fallback logic when the primary relay fails, and more descriptive in-game error messages that distinguish between “relay is down,” “you’re blocked,” and “mod conflict.”

FAQs