Direct answer

Read the missing class name and the first plugin frame in the stack trace. The usual causes are a missing dependency/library or a plugin build compiled for a different server/API/dependency version; install the matching dependency/build rather than adding RAM.

What it means

A plugin tried to load a Java class that is missing from its runtime environment.

If you are a player

  • Record the exact command/message or feature that failed and the time it happened.
  • If the problem affects only your account, note your permissions/group and whether another player can use the same feature.
  • Send the owner the exact wording rather than repeatedly retrying; plugin startup/configuration errors must usually be fixed server-side.

If you run the server

Targeted diagnosis: Find the first NoClassDefFoundError or ClassNotFoundException and record the full missing class name plus the first plugin stack trace. The missing class can point to a required library, wrong API version or incorrect plugin packaging.

  1. Read the first plugin-specific startup exception and identify the exact plugin, dependency/class/method, and server API version involved.
  2. Use a plugin build whose author explicitly supports your current Minecraft/server version and install the documented dependencies.
  3. Remove duplicate/old JAR copies after taking a backup, then restart fully; hot reloads can leave stale classes/state behind.
  4. Do not edit plugin metadata or rename JARs to bypass compatibility checks; that does not backport missing API code.

Fix and verify: Check the plugin’s declared dependencies and its Paper/Bukkit platform build. Replace the incompatible plugin or restore the required dependency at a matching version; do not put random Java libraries into the server root without documentation.

References

Use the documentation for the exact software and release you run. These sources support the settings or diagnostic behavior used in this fix.

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