Bukkit

What steps will reproduce the problem?
1. On server start.

What version of the product are you using?
The last one.

Server Version?
CraftBukkit version git-Bukkit-1.2.5-R4.0-b2222jnks (MC: 1.2.5) (Implementing API version 1.2.5-R4.0)

Do you have an error log of what happened?

[SEVERE] Could not load 'plugins\Player_of_the_Month.jar' in folder 'plugins'
org.bukkit.plugin.InvalidPluginException: java.lang.IllegalArgumentException: File cannot be null
at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:149)
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:213)
at org.bukkit.craftbukkit.CraftServer.<init>(CraftServer.java:189)
at net.minecraft.server.ServerConfigurationManager.<init>(ServerConfigurationManager.java:53)
at net.minecraft.server.MinecraftServer.init(MinecraftServer.java:166)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:432)
at net.minecraft.server.ThreadServerApplication.run(SourceFile:492)
Caused by: java.lang.IllegalArgumentException: File cannot be null
at org.apache.commons.lang.Validate.notNull(Validate.java:203)
at org.bukkit.configuration.file.YamlConfiguration.loadConfiguration(YamlConfiguration.java:170)
at org.bukkit.plugin.java.JavaPlugin.reloadConfig(JavaPlugin.java:117)
at org.bukkit.plugin.java.JavaPlugin.getConfig(JavaPlugin.java:111)
at net.SimplePlugins.PotM.Main.<init>(Main.java:25)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
at java.lang.reflect.Constructor.newInstance(Unknown Source)
at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:145)
... 8 more

Hey! What I have to do so?

HEY!