critical

Java is too old for this software

Q: What does "has been compiled by a more recent version of the Java Runtime (class file version 65.0), this version of the Java Runtime only recognizes class file versions up to 61.0" mean?

Java is too old for this software. The class file version in the error maps directly to a Java release, so the requirement is exact. Install the newer Java version from adoptium.net and point the server at it.

Q: How do I fix "has been compiled by a more recent version of the Java Runtime (class file version 65.0), this version of the Java Runtime only recognizes class file versions up to 61.0"?

1. Translate the number: 65 means install Java 21. 61 means Java 17. 69 means Java 25. The error tells you exactly which. 2. Install that Java: Adoptium (adoptium.net) has every version. Install the JDK or JRE the error asks for alongside the old one; do not remove the old one until the server runs. 3. Point the server at it: On a panel, change the Java version setting. On your own machine, put the new Java first in PATH or call it by full path in the start script. 4. Restart and check java -version in the log: The first lines of a server log print the Java version. Confirm it changed.

What it looks like in your log

has been compiled by a more recent version of the Java Runtime (class file version 65.0), this version of the Java Runtime only recognizes class file versions up to 61.0

What causes it

The class file version in the error maps directly to a Java release, so the requirement is exact.

How to fix it

Install the newer Java version from adoptium.net and point the server at it.

Why it happens

Every compiled Java class carries the version of Java it was compiled for. A runtime refuses to load classes newer than itself. The number in the error maps exactly: 52 is Java 8, 61 is Java 17, 65 is Java 21, 69 is Java 25. "class file version 65.0 ... only recognizes up to 61.0" means the software wants Java 21 and the server is running Java 17.

Minecraft itself moved: 1.17 needs Java 16, 1.18 through 1.20.4 need Java 17, 1.20.5 and later need Java 21. Plugins and mods follow the game, and a plugin built for 1.21 will not load on a Java 17 runtime even if the server jar does.

Fix it step by step

1Translate the number65 means install Java 21. 61 means Java 17. 69 means Java 25. The error tells you exactly which.
2Install that JavaAdoptium (adoptium.net) has every version. Install the JDK or JRE the error asks for alongside the old one; do not remove the old one until the server runs.
3Point the server at itOn a panel, change the Java version setting. On your own machine, put the new Java first in PATH or call it by full path in the start script.
4Restart and check java -version in the logThe first lines of a server log print the Java version. Confirm it changed.

If that didn't work

If the game needs an older Java than a plugin wants, the plugin is built for a newer server version than you run. Update the server or use the plugin build for your version.

The mirror image, "Unsupported class file major version", is Java being too new for a modpack. That has its own page.

Not sure this is your problem? Paste your log and Roastd will tell you which of these it actually matched, and what else it found.

Check your own log