17:28:43 [SEVERE] Could not load 'plugins\OKLoginTiers.jar' in folder 'plugins'
org.bukkit.plugin.InvalidPluginException: java.lang.NoClassDefFoundError: org/bu
kkit/event/player/PlayerListener
        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.CraftServer.loadPlugins(CraftServer.java:227)
        at org.bukkit.craftbukkit.CraftServer.<init>(CraftServer.java:205)
        at net.minecraft.server.ServerConfigurationManagerAbstract.<init>(Server
ConfigurationManagerAbstract.java:51)
        at net.minecraft.server.ServerConfigurationManager.<init>(SourceFile:11)

        at net.minecraft.server.DedicatedServer.init(DedicatedServer.java:111)
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:398)
        at net.minecraft.server.ThreadServerApplication.run(SourceFile:856)
Caused by: java.lang.NoClassDefFoundError: org/bukkit/event/player/PlayerListene
r
        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
Caused by: java.lang.ClassNotFoundException: org.bukkit.event.player.PlayerListe
ner
        at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.
java:34)
        at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.
java:29)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        at java.lang.ClassLoader.loadClass(Unknown Source)
        ... 12 more