Bukkit

When I use /season weather sun or season weather day it results in an error being displayed to the chat.
"An internal error occured while attempting to perform this command"

The following is the message that is put into my console:

12.05 00:37:43 [Multicraft] Skipped 4 lines due to rate limit (30/s)
12.05 00:37:35 [Server] INFO at org.bukkit.plugin.java.PluginClassLoader.findClass0(PluginClassLoader.java:70)
12.05 00:37:35 [Server] INFO Caused by: java.lang.ClassNotFoundException: net.minecraft.server.v1_5_R2.World
12.05 00:37:35 [Server] INFO ... 15 more
12.05 00:37:35 [Server] INFO at org.bukkit.command.PluginCommand.execute(PluginCommand.java:44)
12.05 00:37:35 [Server] INFO at org.rominos2.Seasons.Seasons.onCommand(Seasons.java:105)
12.05 00:37:35 [Server] INFO at org.rominos2.Seasons.SeasonsCommands.playerCommand(SeasonsCommands.java:36)
12.05 00:37:35 [Server] INFO at org.rominos2.Seasons.SeasonsCommands.weather(SeasonsCommands.java:150)
12.05 00:37:35 [Server] INFO at org.rominos2.Seasons.Managers.SeasonsManager.changeWeather(SeasonsManager.java:174)
12.05 00:37:35 [Server] INFO at org.rominos2.Seasons.Managers.SnowManager.SeasonsSnowManager.onWeatherChange(SeasonsSnowManager.java:58)
12.05 00:37:35 [Server] INFO at org.rominos2.Seasons.Managers.SnowManager.SeasonsSnowManager.start(SeasonsSnowManager.java:67)
12.05 00:37:35 [Server] INFO Caused by: java.lang.NoClassDefFoundError: net/minecraft/server/v1_5_R2/World
12.05 00:37:35 [Server] INFO at net.minecraft.server.v1_5_R3.ThreadServerApplication.run(SourceFile:573)
12.05 00:37:35 [Server] INFO at net.minecraft.server.v1_5_R3.MinecraftServer.run(MinecraftServer.java:410)
12.05 00:37:35 [Server] INFO at net.minecraft.server.v1_5_R3.MinecraftServer.q(MinecraftServer.java:477)
12.05 00:37:35 [Server] INFO at net.minecraft.server.v1_5_R3.DedicatedServer.r(DedicatedServer.java:226)
12.05 00:37:35 [Server] INFO at net.minecraft.server.v1_5_R3.MinecraftServer.r(MinecraftServer.java:581)
12.05 00:37:35 [Server] INFO at net.minecraft.server.v1_5_R3.DedicatedServerConnection.b(SourceFile:30)
12.05 00:37:35 [Server] INFO at net.minecraft.server.v1_5_R3.ServerConnection.b(SourceFile:35)
12.05 00:37:35 [Server] INFO at net.minecraft.server.v1_5_R3.PlayerConnection.d(PlayerConnection.java:110)
12.05 00:37:35 [Server] INFO at net.minecraft.server.v1_5_R3.NetworkManager.b(NetworkManager.java:292)
12.05 00:37:35 [Server] INFO at net.minecraft.server.v1_5_R3.Packet3Chat.handle(Packet3Chat.java:44)
12.05 00:37:35 [Server] INFO at net.minecraft.server.v1_5_R3.PlayerConnection.a(PlayerConnection.java:841)
12.05 00:37:35 [Server] INFO at net.minecraft.server.v1_5_R3.PlayerConnection.chat(PlayerConnection.java:884)
12.05 00:37:35 [Server] INFO at net.minecraft.server.v1_5_R3.PlayerConnection.handleCommand(PlayerConnection.java:966)
12.05 00:37:35 [Server] INFO at org.bukkit.craftbukkit.v1_5_R3.CraftServer.dispatchCommand(CraftServer.java:523)
12.05 00:37:35 [Server] INFO at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:189)
12.05 00:37:35 [Server] INFO at org.bukkit.command.PluginCommand.execute(PluginCommand.java:46)
12.05 00:37:35 [Server] INFO org.bukkit.command.CommandException: Unhandled exception executing command 'season' in plugin Seasons v2.0.2
12.05 00:37:35 [Server] SEVERE null