my server is not working when y want to turn on, it put me that:

2021-09-22 17:28:38,357 main ERROR Error processing element Queue ([Appenders: null]): CLASS_NOT_FOUND
2021-09-22 17:28:38,420 main WARN Advanced terminal features are not available in this environment
2021-09-22 17:28:38,514 main ERROR Unable to locate appender "ServerGuiConsole" for logger config "root"
[17:28:38] [main/INFO] [cp.mo.mo.Launcher/MODLAUNCHER]: ModLauncher running: args [--gameDir, ., --launchTarget, fmlserver, --fml.forgeVersion, 36.2.4, --fml.mcpVersion, 20210115.111550, --fml.mcVersion, 1.16.5, --fml.forgeGroup, net.minecraftforge, nogui]
[17:28:38] [main/INFO] [cp.mo.mo.Launcher/MODLAUNCHER]: ModLauncher 8.0.9+86+master.3cf110c starting: java version 1.8.0_301 by Oracle Corporation
[17:28:39] [main/INFO] [ne.mi.fm.lo.FixSSL/CORE]: Added Lets Encrypt root certificates as additional trust
Exception in thread "main" [17:28:39] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:-1]: java.lang.NoClassDefFoundError: com/google/common/collect/ImmutableList
[17:28:39] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:-1]:         at org.spongepowered.asm.mixin.MixinEnvironment$Phase.<clinit>(MixinEnvironment.java:99)
[17:28:39] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:-1]:         at org.spongepowered.asm.service.MixinServiceAbstract.getInitialPhase(MixinServiceAbstract.java:87)
[17:28:39] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:-1]:         at org.spongepowered.asm.launch.MixinBootstrap.start(MixinBootstrap.java:141)
[17:28:39] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:-1]:         at org.spongepowered.asm.launch.MixinTransformationService.initialize(MixinTransformationService.java:84)
[17:28:39] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:-1]:         at cpw.mods.modlauncher.TransformationServiceDecorator.onInitialize(TransformationServiceDecorator.java:68)
[17:28:39] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:-1]:         at cpw.mods.modlauncher.TransformationServicesHandler.lambda$initialiseTransformationServices$7(TransformationServicesHandler.java:107)
[17:28:39] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:-1]:         at java.util.HashMap$Values.forEach(Unknown Source)
[17:28:39] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:-1]:         at cpw.mods.modlauncher.TransformationServicesHandler.initialiseTransformationServices(TransformationServicesHandler.java:107)
[17:28:39] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:-1]:         at cpw.mods.modlauncher.TransformationServicesHandler.initializeTransformationServices(TransformationServicesHandler.java:59)
[17:28:39] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:-1]:         at cpw.mods.modlauncher.Launcher.run(Launcher.java:76)
[17:28:39] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:-1]:         at cpw.mods.modlauncher.Launcher.main(Launcher.java:66)
[17:28:39] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:-1]:         at net.minecraftforge.server.ServerMain$Runner.runLauncher(ServerMain.java:63)
[17:28:39] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:-1]:         at net.minecraftforge.server.ServerMain$Runner.access$100(ServerMain.java:60)
[17:28:39] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:-1]:         at net.minecraftforge.server.ServerMain.main(ServerMain.java:57)
[17:28:39] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:-1]: Caused by: java.lang.ClassNotFoundException: com.google.common.collect.ImmutableList
[17:28:39] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:-1]:         at java.net.URLClassLoader.findClass(Unknown Source)
[17:28:39] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:-1]:         at java.lang.ClassLoader.loadClass(Unknown Source)
[17:28:39] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:-1]:         at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
[17:28:39] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:-1]:         at java.lang.ClassLoader.loadClass(Unknown Source)
[17:28:39] [main/INFO] [STDERR/]: [java.lang.ThreadGroup:uncaughtException:-1]:         ... 14 more
 

Quote

NoClassDefFoundError: com/google/common/collect/ImmutableList

did you run the initial setup? that class is in guava lib, which comes by default in MDK, so it should be there... do you see it in your IDE? 

well, mainly running 'gradle build'... that's the task that should pull down all the lib dependencies ... more details https://mcforge.readthedocs.io/en/latest/gettingstarted/

lol, sowwy, I thought it was the one who created the post that was answering to my reply 😛