[00:29:34 WARN]: Exception in thread "Craft Scheduler Thread - 3"
[00:29:34 WARN]: org.apache.commons.lang.UnhandledException: Plugin KnockbackMaster v2.14.2 generated an exception while executing task 76
        at org.bukkit.craftbukkit.v1_7_R4.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:56)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.NoClassDefFoundError: com/google/gson/JsonElement
        at com.xdefcon.knockbackmaster.KnockbackMaster.a(KnockbackMaster.java:36)
        at org.bukkit.craftbukkit.v1_7_R4.scheduler.CraftTask.run(CraftTask.java:71)
        at org.bukkit.craftbukkit.v1_7_R4.scheduler.CraftAsyncTask.run(CraftAsyncTask.java:53)
        ... 3 more
Caused by: java.lang.ClassNotFoundException: com.google.gson.JsonElement
        at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
        at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:101)
        at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.java:86)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
        ... 6 more