Minecraft Error Codes List (and How to Fix Them)

Before you re-install, try the options mentioned below!

Minecraft is one of the most popular games in the world and has many players facing one of many errors when they try to play the game. The list below provides the solutions and workarounds to some of the most common error codes players run into.

Minecraft Error Codes List (and How to Fix Them)

This is a comprehensive list, so we'll try to keep the solutions and workarounds concise. No one wants to run into more problems when they're trying to fix one already!

Multiplayer Errors

These are issues you will only face when you're online or trying to connect to a server.

Connection refused: connect

  • Possible Causes
    • The IP:Port you entered is invalid.
    • The server itself is inaccessible.
  • Possible Solutions
    • Confirm you've entered the correct server address and try again.

Related: Minecraft Iron, Gold, and Copper Will Drop Raw Ore in the 1.17 Caves and Cliffs Update - Pro Game Guides

End of stream

  • Possible Causes
    • The server is not sending information to the client.
  • Possible Solutions
    • Restart Minecraft or the server.
    • Confirm both the server and the client have good internet connection.

Failed to login: Bad Login

  • Possible Causes
    • You've attempted to log in too quickly after your previous attempt.
  • Possible Solutions
    • Confirm that you are running the same version of Minecraft as the server.
    • Check your network connection.
    • Wait a few minutes before trying to log in again.

Failed to login: invalid IP

  • Possible Causes
    • The Mojang servers cannot validate your IP address.
  • Possible Solutions
    • Try again later when validation services have returned to normal.
    • Check your internet connection to make sure there are no dropped packets.

Failed to login: the authentication servers are currently down for maintenance

  • Possible Causes
    • The Minecraft server could not contact the authentication server for the user logging in.
  • Possible Solutions
    • Try again later when the authentication servers return to normal.
    • Check your firewall to make sure the servers are not blocked.
    • Set the server.properties to online-mode=false. This disables authentication for the server.

Internal Exception: io.netty.handler.timeout.ReadTimeoutException

  • Possible Causes
    • The game our your computer can't process the data from the server fast enough, forcing you to fall out of sync with the server.
  • Possible Solutions
    • Check your internet connection to make sure there are no dropped packets.
    • Make sure your computer is fast enough to run the game. It takes more processing power to play it on a server than in single player.

java.io.IOException: Server returned HTTP response code: 503

  • Possible Causes
    • The server cannot authenticate your account because minecraft.net is down.
  • Possible Solutions
    • Try again later when the Minecraft authentication servers have returned to normal.

java.net.SocketException: Connection reset

  • Possible Causes
    • The server has shut down or using an excessive amount of processing power.
    • The user's internet connection forced them to disconnect from the server.
  • Possible Solutions
    • Wait a few minutes and try to reconnect to the server.
    • Confirm the server connection is normal.

Outdated client!

  • Possible Causes
    • Your Minecraft client is using an older version than the client the server is using.
  • Possible Solutions
    • Update your Minecraft client to the version the server is using.

Outdated server!

  • Possible Causes
    • Your Minecraft client is using a newer version than the client the server is using.
  • Possible Solutions
    • In the Minecraft Launcher, change your Minecraft version to the one being used by the server.

This server responded with an invalid server key.

  • Possible Causes
    • An attempt to validate a modified server has returned with an incorrect value.
  • Possible Solutions
    • Attempt to log in again.

Took too long to log in.

  • Possible Causes
    • The server cannot authenticate who you are because minecraft.net wasn't responding
  • Possible Solutions
    • Confirm your internet connection works properly, and that there is no loss of connection.
    • Wait a few minutes and try again.

User Not Premium

  • Possible Causes
    • Your Minecraft client does not pass the minecraft.net authentication.
  • Possible Solutions
    • Confirm your client is a paid version of the game, rather than a hacked or modified client.

You are not whitelisted on this server

  • Possible Causes
    • You are not on the list of people who may connect to the server.
  • Possible Solutions
    • Contact the server owner/administrator and request to be added to the list of people who may connect to the server.

Related: How to Install Pixelmon - Pro Game Guides


These issues can happen either in Single Player or Multiplayer and usually result in the game shutting down.

Failed to check session lock, aborting

  • Possible Causes
    • An active lock on part of the world that a third party editor has left locked.
  • Possible Solutions
    • Delete session.lock in the world save folder.


  • Possible Causes
    • This is a catch-all crash response. There are many error logs that could cause this. The game client crashed on startup.
  • Possible Solutions
    • Find the Java crash log (look for a file on your desktop that looks similar to: hs_err_pid). Check for the exact error code there.
    • If you're unable to determine the problem and it persists, rename the .minecraft directory to something else. Start Minecraft again and start a new game. This will create a new .minecraft directory. If necessary, move the saved worlds to the new .minecraft/saves folder.

Runtime Errors

These are errors with the game understanding the code while the game is running. These may be caused by changes made to the code or issues with the way your game/world is saved.


  • Possible Causes
    • Your world may be corrupted.
    • There is invalid JSON/NBT formatting in your save files; tag names are defined as a "variable" instead of a string.
  • Possible Solutions
    • Restore your save to a previous backup and remove any mods that you didn't have before this issue.


  • Possible Causes
    • Your game has run out of memory.
  • Possible Solutions
    • Increase the amount of memory that is allocated to java.
    • Free up memory by closing down any other unused programs.
    • Reduce the number of mods that use excessive amounts of computer memory.

RuntimeException: No OpenGL context found in the current thread.

  • Possible Causes
    • Your graphics card or driver cannot run Minecraft.
  • Possible Solutions
    • Make sure your graphics driver is up-to-date.
    • On Linux systems, install a package that contains the xrandr utility.
    • Upgrade your graphics card to something more powerful.

These are the most common error codes that players face. If you have one that isn't listed above, be sure to let us know in the comments below!

Want to improve the look of your Minecraft game? Use our guides on How to Install OptiFine and How to Install BSL Shaders!

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  1. well, this is the one im getting, can i get some help
    Error: java.lang.NoClassDefFoundError: cer
    Exit Code: -1

    1. im also getting this one. (many times) couldn’t fix it either. just starting a new world helps but ofcourse u lose all the progress of that previous world.