Code:

package de.nutellakissen.main;

import org.bukkit.plugin.java.JavaPlugin;

public class ErstesPlugin extends JavaPlugin{


    public void onEnable() {

    System.out.println("ErstesPlugin erfolgreich gestartet.");

    }


}













plugin.yml:

main: de.nutellakissen.main
name: NutellaKissen
version: 1.0
author: NutellaKissen
description: 1st Plugin




















Der genaue Fehler:  Could not load 'plugins\plugin.jar' in folder 'plugins'
org.bukkit.plugin.InvalidDescriptionException: Invalid plugin.yml
        at org.bukkit.plugin.java.JavaPluginLoader.getPluginDescription(JavaPluginLoader.java:154) ~[spigot-1.8.8-R0.1-SNAPSHOT.jar:git-Spigot-21fe707-e1ebe52]
        at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager.java:133) [spigot-1.8.8-R0.1-SNAPSHOT.jar:git-Spigot-21fe707-e1ebe52]
        at org.bukkit.craftbukkit.v1_8_R3.CraftServer.loadPlugins(CraftServer.java:292) [spigot-1.8.8-R0.1-SNAPSHOT.jar:git-Spigot-21fe707-e1ebe52]
        at org.bukkit.craftbukkit.v1_8_R3.CraftServer.reload(CraftServer.java:739) [spigot-1.8.8-R0.1-SNAPSHOT.jar:git-Spigot-21fe707-e1ebe52]
        at org.bukkit.Bukkit.reload(Bukkit.java:535) [spigot-1.8.8-R0.1-SNAPSHOT.jar:git-Spigot-21fe707-e1ebe52]
        at org.bukkit.command.defaults.ReloadCommand.execute(ReloadCommand.java:25) [spigot-1.8.8-R0.1-SNAPSHOT.jar:git-Spigot-21fe707-e1ebe52]
        at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:141) [spigot-1.8.8-R0.1-SNAPSHOT.jar:git-Spigot-21fe707-e1ebe52]
        at org.bukkit.craftbukkit.v1_8_R3.CraftServer.dispatchCommand(CraftServer.java:641) [spigot-1.8.8-R0.1-SNAPSHOT.jar:git-Spigot-21fe707-e1ebe52]
        at org.bukkit.craftbukkit.v1_8_R3.CraftServer.dispatchServerCommand(CraftServer.java:627) [spigot-1.8.8-R0.1-SNAPSHOT.jar:git-Spigot-21fe707-e1ebe52]
        at net.minecraft.server.v1_8_R3.DedicatedServer.aO(DedicatedServer.java:412) [spigot-1.8.8-R0.1-SNAPSHOT.jar:git-Spigot-21fe707-e1ebe52]
        at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:375) [spigot-1.8.8-R0.1-SNAPSHOT.jar:git-Spigot-21fe707-e1ebe52]
        at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:654) [spigot-1.8.8-R0.1-SNAPSHOT.jar:git-Spigot-21fe707-e1ebe52]
        at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:557) [spigot-1.8.8-R0.1-SNAPSHOT.jar:git-Spigot-21fe707-e1ebe52]
        at java.lang.Thread.run(Unknown Source) [?:1.8.0_131]
Caused by: java.io.FileNotFoundException: Jar does not contain plugin.yml
        ... 14 more