(tl;dr: Try installing a different Java JDK!)
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So yeah, this isn’t actually an “I need help” thread, because thankfully I’ve managed to solve this…but I figured I’d leave my experience here, in case anyone else is having similar struggles and is searching for an answer online.
Recently, I was having a very annoying error that I’d never seen before while using a custom mod list. My Forge (version 47.1.3 – I’m stuck with this, because it’s the only one that is compatible with the Sinytra Connector mod) would get to the stage “Mod loading: dispatching sided\_setup”, and then the message “Error during mod loading” would show up in the bottom left corner. Eventually, after about a minute or so, the game crashed, ostensibly because of the Let’s Do Vinery mod:
*”Crash: Vinery encountered an error during the sided\_setup phase Java.lang.ArrayIndexOutOfBoundsException: index 4096 out of bounds for length 2049″*
Now, here’s the strange thing. To temporarily “fix” this, I found that all I had to do was close Minecraft, reopen it, and (most of the time) it would magically work again. But annoyingly, this solution didn’t last forever – I always had to sit through at least one initial crash and reload process every time I booted the game. Removing the Vinery mod (and all the other Let’s Do mods), booting the game, and then re-adding them back again afterwards didn’t solve anything. Infuriatingly, I could find no solution on Reddit (although [numerous poor souls were having similar problems](https://www.reddit.com/r/MinecraftHelp/comments/16zb39v/encountered_an_error_during_the_sided_setup_event/)), and the error log was completely opaque to me.
What worked for me, at long last, had nothing to do with re-installing different versions of the mod, or changing anything about my Minecraft installation. I actually had to switch to a different Java JDK version altogether. I had been using the most recent version of Eclipse Temerin (21) – once I changed to the older [LTS 17 version](https://adoptium.net/temurin/releases/?version=17), no more “sided\_setup” errors, no more crashes. Hallelujah! So if you’re in the same boat as me, try giving this a shot – hopefully it will fix your problem too.
If Temerin version 17 specifically still doesn’t work, then try other versions of Java. I can’t guarantee that my solution will work for everyone experiencing this error, because I don’t know for sure why it was happening in the first place…but I suspect that perhaps a race condition in some mods may be causing them to behave differently on various computing environments (due to differing CPU speeds and memory architectures). This could explain why [two people with the same modpack and the same version of Java may not experience the same crash](https://www.reddit.com/r/Minecraft/comments/1290n59/mod_encountered_an_error_during_the_sided_setup/).
by Falalalally