Server Edition Bug: Server Crash upon joining.

[Ryan5521]

What happened?

When I join my Fabric server, the server crashes during the login process while sending the command tree to the client.

The crash happens consistently on player join and points to PermissionManager.canManageAliases() inside Nek's Command Maker.

Which Loader and Minecraft Version?

Fabric
Minecraft Version 1.21.11

Which Mod Versions did I test?

4.0.0-beta.3
3.2.1-1.21x

My suspicion

The crash appears to be caused by a NoSuchMethodError:

java.lang.NoSuchMethodError: 'boolean net.minecraft.server.command.ServerCommandSource.method_9259(int)'

My guess is that the mod is calling a Minecraft method that no longer exists (or whose signature changed) in Minecraft 1.21.11 (even though the mod is for 1.21.11!). This would explain why the crash occurs as soon as the command tree is being built and permission checks are performed.

The crash report is attached.
crash-2026-07-09_12.36.49-server.txt.txt

[Ryan5521]

I hope this helps you find the bug better :D

[Ryan5521]

Possible cause

I noticed that another mod fails with the exact same NoSuchMethodError on Minecraft 1.21.11, also when checking command permissions.

Minecraft 1.21.11 appears to have changed the permission API (ServerCommandSource). The old hasPermissionLevel(int) method (method_9259) no longer exists with the same signature, causing a NoSuchMethodError when the mod performs a permission check.

So yeah, idk what to do here, I'm not into coding mods but maybe now you know how to fix it!

[lucgei231]

Sorry about this! A possible temporary fix is to remove LuckPerms from your server or any other permission mod. I am currently on holiday in Amerixa so I will not be able to fix the mod until Saturday or Sunday next week. Very sorry about this, will look into it soon!

-Nekky9180

[lucgei231]

Also I may have overlooked this issue as when I test the mod, I run it on Fabric 1.21.9 and fabric 26.1.2. Not Fabric 1.21.11.

-Nekky

[Ryan5521]

Thanks for the quick reply!

No worries, enjoy your holiday :D

Just to clarify: I'm not using LuckPerms or any other permissions mod on the server, so the crash seems to be caused by Command Maker itself.

And yes, I can confirm that I'm running Minecraft 1.21.11 (Fabric Loader 0.19.3 / Fabric API 0.141.4).

Hopefully that helps narrow it down. Thanks again for looking into it!