What is the difference between NoClassDefFoundError and ClassNotFoundException?

ClassNotFoundException occurs when the application tries to load a class that cannot be found, while NoClassDefFoundError occurs when the class was present at compile time but is missing at runtime.

Can I fix this by changing my RAM settings?

No, these errors are related to missing or incompatible files, not the amount of RAM allocated to your server.

Do I need to restart my server after deleting a problematic plugin?

Yes, you must restart your server for any changes to the plugins or mods folder to take effect.

Where can I find the specific file causing the error?

The error will usually be printed in your latest.log file, which will point to the specific plugin or mod causing the crash.

Fixing java.lang.NoClassDefFoundError in Minecraft

Understanding the Error

java.lang.NoClassDefFoundError and java.lang.ClassNotFoundException are common Java errors that occur when the server attempts to load a class that is missing from the classpath. In the context of a Minecraft server, this usually means a plugin, mod, or library file is either corrupted, incompatible with your server version, or missing a required dependency.

How to fix it

1. Check for missing dependencies

Many plugins require other plugins (like Vault or ProtocolLib) to function. If you have installed a plugin without its required dependencies, the server will fail to load the class.

On AwakeNode: Use the File Manager to inspect your plugins folder. Ensure all required dependencies are present and match the versions specified by the plugin developer.
On other hosts: Use an SFTP client like FileZilla to browse your server files and verify that all dependency JAR files are present in the plugins or mods directory.

2. Verify plugin and mod compatibility

Using a plugin or mod designed for a different Minecraft version often leads to class errors. Ensure every file in your plugins or mods folder is compatible with your current server version.

On AwakeNode: Check the files in your plugins or mods folder in the Files tab, and replace any that aren't built for your server software and Minecraft version.
On other hosts: Manually download the correct versions from official sources (SpigotMC, Modrinth, or CurseForge) and replace the incompatible files.

3. Clear corrupted files

Sometimes a file can become corrupted during an upload or update.

On AwakeNode: Delete the problematic plugin or mod via the File Manager and re-upload a fresh copy.
On other hosts: Delete the JAR file from your server directory and upload a fresh copy using SFTP.

4. Contact Support

If you have verified your files and the error persists, it may be related to the Java environment or startup configuration.

On AwakeNode: Open a ticket. To add your own JVM flags, set a custom startup command in your server's tab.

java.lang.NoClassDefFoundError / ClassNotFoundException