How To Fix "A Proxy Plugin Caused An Illegal Protocol State" - Minecraft

​Running a Minecraft server through a proxy can unlock tons of flexibility, but sometimes errors pop up that leave players scratching their heads. One of the more confusing ones is the dreaded “A Proxy Plugin Caused an Illegal Protocol State” Minecraft error message.

This error usually signals a plugin miscommunication between the proxy and the backend server. The good news? It’s fixable. By checking your setup and making a few targeted adjustments, you can get your server running smoothly again. In this guide, we’ll walk through the most common causes and practical fixes, including:

• Identifying plugin conflicts

• Updating proxy/server versions

• Adjusting chat or message-related plugins

• Testing connections step by step

What Is The "Proxy Plugin Caused An Illegal Protocol State" Error?

The “Proxy Plugin Caused an Illegal Protocol State” error in Minecraft occurs when a proxy plugin tries to modify or cancel signed chat messages, violating the game’s chat signing rules. To fix it, ensure all plugins are updated to the latest version.

Why Does The "Proxy Plugin Caused An Illegal Protocol State" Error Happen?

• A proxy plugin tried to modify messages or cancel a signed chat, which violates the game’s chat signing rules.

• The backend server and proxy (like Velocity) are running different versions or incompatible plugins, causing an illegal protocol state.

• Outdated plugins or a velocity issue can trigger the error when handling chat messages or commands.

How To Fix The "Proxy Plugin Caused An Illegal Protocol State" Error

To fix the “Proxy Plugin Caused an Illegal Protocol State” error in Minecraft, make sure your proxy plugin and all related plugins are updated to the latest version. Check that your backend server and proxy (like Velocity) are running compatible versions, and ensure any modded clients are supported.

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Updated on: 09/09/2025