Shared Thu, 04 Jun 2026 06:32:44 GMT·Auto-expires 7/4/2026
Wrong Java version
Forge 47.3.0MC 1.20.1
What happened
The Java runtime on this server is newer than the one the mod was compiled for.
Try this first
Open Settings → Java version and pick the older Java that matches the modpack's Minecraft version (1.7-1.12 → Java 8, 1.13-1.16 → Java 11/17, 1.17+ → Java 17, 1.20.5+ → Java 21).
Where we saw it
---- Minecraft Crash Report ---- Time: 2026-05-22 09:14:11 Description: Exception in server tick loop java.lang.UnsupportedClassVersionError: com/example/Foo 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 -- System Details -- Minecraft Version: 1.20.1 Forge: net.minecraftforge:47.3.0 Operating System: Linux (amd64) version 6.8.0