3:26:21 [WARNING] Error enabling plugin GadgetsMenu
java.lang.NoClassDefFoundError: org/bukkit/plugin/java/JavaPlugin
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(Unknown Source)
    at java.security.SecureClassLoader.defineClass(Unknown Source)
    at java.net.URLClassLoader.defineClass(Unknown Source)
    at java.net.URLClassLoader.access$100(Unknown Source)
    at java.net.URLClassLoader$1.run(Unknown Source)
    at java.net.URLClassLoader$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(Unknown Source)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at net.md_5.bungee.api.plugin.PluginClassloader.loadClass0(PluginClassloader.java:34)
    at net.md_5.bungee.api.plugin.PluginClassloader.loadClass(PluginClassloader.java:27)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    at net.md_5.bungee.api.plugin.PluginManager.enablePlugin(PluginManager.java:304)
    at net.md_5.bungee.api.plugin.PluginManager.loadPlugins(PluginManager.java:212)
    at net.md_5.bungee.BungeeCord.start(BungeeCord.java:264)
    at net.md_5.bungee.BungeeCordLauncher.main(BungeeCordLauncher.java:55)
    at net.md_5.bungee.Bootstrap.main(Bootstrap.java:15)
Caused by: java.lang.ClassNotFoundException: org.bukkit.plugin.java.JavaPlugin
    at net.md_5.bungee.api.plugin.PluginClassloader.loadClass0(PluginClassloader.java:53)
    at net.md_5.bungee.api.plugin.PluginClassloader.loadClass(PluginClassloader.java:27)
    at java.lang.ClassLoader.loadClass(Unknown Source)
    ... 18 more