How to fix Minecraft Internal Exception Error (io.netty.handler or Java.IO.IOException)

While Minecraft isn't one of the most graphically intensive games, it can still cause problems for players; especially those trying to play multiplayer on MC servers.

For those facing the error with Internal Exception while trying to connect to a MC server, it can be challenging to fix it. This can be due to several different reasons.

This guide will dive into the best ways players can hopefully fix Minecraft Internal Exception error when trying to play the game.

How do you fix Minecraft Internal Exception Error (io.netty.handler) (Java.IO.IOException) errors?

Simply put, a connection problem causes Minecraft Internal Exception error. This could be due to several things. Players can try each of the standard solutions listed below to see if one happens to rectify the issue.

First, check if the server you are trying to join has an error

Players should first check whether the connection issue causing the Internal Exception error message is coming from the server or their side.

If the error is from the server-side, players can rest assured that nothing is wrong with their copy of Minecraft or their PC settings. It is simply a problem with the server itself.

The best way to check if the server has an error is by connecting to this testing server with IP: test.prisonfun.com

If the connection to this server is successful, there is no problem with the game client or PC settings. This particular server supports all versions of the game and is always up to date, so it is the best place to test any potential connection problems.

If the connection to this server is unsuccessful, then there is an issue on the player's side, not the server. Players can try the proposed solutions below to try and fix them.

Update Java to fix Minecraft Internal Exception Error

Minecraft is a Java application and needs Java to run. Players should ensure they have the latest official Java version:

Go to the official Java Download found here
Download the latest version of Java available
Complete the installation
Retry on Minecraft to join server IP: test.prisonfun.com

Turn off Firewall + Antivirus + VPN

Minecraft multiplayer is sensitive to specific Firewall rules, Antivirus settings and VPNs.

Players can try and disable all three of these and retry the connection:

Turn off firewall

Press Windows Key + R (or type "run" in the start menu)
Type "control" in the Run menu and hit enter
Press "System and Security"
Press "Windows Firewall"
On the left-hand side, press "Turn windows defender firewall on or off"
Turn off the firewall for both public and private network
Retry on MC to join server IP: test.prisonfun.com

Turning off the antivirus and VPN is less straightforward than turning off the firewall. It will depend on the specific antivirus and VPN being used.

Turn off AntiVirus

If players are using a specific type of antiviruses such as Norton, McAffee, or Avast, they must be fully disabled in their control panels. After doing this, players can retry to connect to the server IP: test.prisonfun.com

Turn off VPN

If players are connected to any VPN, it should be turned off and disconnected. After doing this, players can retry their connection to the server IP: test.prisonfun.com

Change DNS Server Address to fix Minecraft Internal Exception Error

The DNS server can have an impact on failed connections. It is important to make sure it is up to date and accurate.

Press Windows Key + R (or type "run" in the start menu)
Type "control" in the Run menu and hit enter
Navigate to the "Network and internet" tab
Press "Network and sharing center"
Select the connection (usually either "Ethernet" or "wifi")
Press "Properties"
Click "Internet Protocol Version 4" (IPv4)
Select "Use the following DNS server addresses"
For the primary DNS server, use 8.8.8.8
For an alternate DNS server, use 8.8.4.4
Press "OK"
Retry on Minecraft to join server IP: test.prisonfun.com

Users may want to watch this video below on how to change the DNS server (it works for Windows 10 and 11).

Re-download a fresh Installation of Minecraft

There may be something wrong with the game installation. Players should try to re-download a fresh copy with no modifications enabled.

Open the official Minecraft launcher (download it here if you don't have it)
On the main launcher menu, click the "Installations" button (it should be at the top of the screen on the navbar)
Press "New installation"
Select the version of Minecraft you want to use (Latest release is recommended)
Press the green "Create" button on the bottom right of the installation menu
Make sure the newly created version is selected on the main launcher menu
Hit the big green "Play" button on the main launcher menu
Retry on Minecraft to join server IP: test.prisonfun.com

Install Minecraft to a new directory

If re-downloading a fresh installation of the gameis unsuccessful, players can try and install a new game directory altogether.

Open the official MC launcher (download it here if you don't have it)
On the main launcher menu, click the "Installations" button (it should be at the top of the screen on the navbar)
Press "New installation"
Select the version of the game you want to use (Latest release is recommended)
For the "Game Directory" option, press "Browse" and select any place where you want to install the game on your PC if you don't know where just press "Desktop" at the top.
Hit OK
Press the green "Create" button on the bottom right to create the new installation profile
Make sure the newly created installation profile is selected on the main launcher menu before launching the game
Hit the big green "Play" button on the main launcher menu
Retry on MC to join server IP: test.prisonfun.com

Try VPN or a different wifi network to fix Minecraft Internal Exception Error

If nothing has worked so far, there might be an issue with the local network. Players can confirm if this is the case by connecting to a different wifi network or simply via a free VPN downloaded online.

Players are free to use their VPN, or they can try out the one in the video tutorial below.

After a VPN is connected to it, players can once again try and connect to the test server IP: test.prisonfun.com

Enable Java Native Sandbox

Enabling the Java Native Sandbox option has helped some users clear up their issues related to io.netty.handler and Java.IO.IOException.

Press the Windows key (or click the start menu icon)
Type Configure Java and press enter
Navigate to the "Advanced" tab and scroll down to the "Advanced security settings" and enable the option "enable the operating system's restricted environment (native sandbox)."
Press Apply, then press OK
Reboot the PC. This is very important.
Retry on Minecraft to join server IP: test.prisonfun.com

Restart Router

Sometimes, the connection problem can originate from the local router needing a reboot. This is for various technical reasons, but restarting a router can assign a new IP and much more, which can help fix the Minecraft Internal Exception error.

Unplug the network router
Wait a few minutes (restart your computer during this time)
Plugin the network router
Retry on MC to join server IP: test.prisonfun.com

Ensure there are no parental or admin restrictions on the PC/Network

Another major cause of the Minecraft Internal Exception error (io.netty.handler and Java.IO.IOException problems) is due to restrictions that are applied by parental control software (e.g., NetNanny, Norton Family, Qustodio, etc...) and network administrators.

Unfortunately, the only way to fix this is to turn them off entirely, which varies in each case due to different software being used.

Should players be aware that parental or admin restrictions are applied to the machine or network, these could most certainly be the underlying cause of the problems.

Once these restrictions are fully turned off, players can once again try and connect to the server with IP: test.prisonfun.com

Edited by Srijan Sen