bukkit - punishmental not loading

19:26:51 [SCHWERWIEGEND] Could not load 'plugins\Punishmental.jar' in folder 'pl
ugins'
org.bukkit.plugin.InvalidPluginException: java.lang.SecurityException: sealing v
iolation: can't seal package sss.RjSowden.Fall: already loaded
        at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.j
ava:154)
        at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.
java:305)
        at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager
.java:230)
        at org.bukkit.craftbukkit.v1_4_6.CraftServer.loadPlugins(CraftServer.jav
a:278)
        at org.bukkit.craftbukkit.v1_4_6.CraftServer.<init>(CraftServer.java:256
)
        at net.minecraft.server.v1_4_6.PlayerList.<init>(PlayerList.java:56)
        at net.minecraft.server.v1_4_6.DedicatedPlayerList.<init>(SourceFile:11)

        at net.minecraft.server.v1_4_6.DedicatedServer.init(DedicatedServer.java
:106)
        at net.minecraft.server.v1_4_6.MinecraftServer.run(MinecraftServer.java:
433)
        at net.minecraft.server.v1_4_6.ThreadServerApplication.run(SourceFile:84
9)
Caused by: java.lang.SecurityException: sealing violation: can't seal package ss
s.RjSowden.Fall: already loaded
        at java.net.URLClassLoader.getAndVerifyPackage(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 org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.
java:44)
        at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.
java:29)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(Unknown Source)
        at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.j
ava:143)
        ... 9 more