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javaminecraft-forge

Forge1.20.4 - Error at blockState class in unClient

I am new to Minecraft modding, and I followed this tutorial to setup my modding: https://www.youtube.com/watch?v=55qUIf3GMss

The user in the video takes the Forge files, builds Gradle with IntelliJ, Java SDK, Parchment, and then runs via runClient. I have followed this step-by-step, and my Gradle builds. However, when I run runClient, I get this error:

Caused by: java.lang.ClassFormatError: Duplicate method name "lambda$static$34" with signature "(Lnet.minecraft.world.level.block.state.BlockState;)I" in class file net/minecraft/world/level/block/Blocks

Here is the log from the point of error: https://pastebin.com/embed_js/m714S8W6

Solution

  • The issue had to do with mappings of Parchment and the Minecraft version. I followed the instructions at the bottom of the Parchment webpage, which go over what to do if the Parchment mapping version doesn't match your Minecraft version.

    I needed to change 2023.12.10-1.20.2 to 1.20.2-2023.12.10-1.20.4 since I am using parchment version 1.20.2 (the latest as of writing) and my Minecarft version is 1.20.4.