MA Error

[SEVERE] Error occurred while enabling MobArena v0.94.3.1 (Is it up to date?): spawnMonsters
java.lang.NoSuchFieldError: spawnMonsters
	at com.garbagemule.MobArena.Arena.<init>(Arena.java:155)
	at com.garbagemule.MobArena.ArenaMaster.loadArenas(ArenaMaster.java:252)
	at com.garbagemule.MobArena.ArenaMaster.initialize(ArenaMaster.java:186)
	at com.garbagemule.MobArena.MobArena.onEnable(MobArena.java:79)
	at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:126)
	at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:920)
	at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:280)
	at org.bukkit.craftbukkit.CraftServer.loadPlugin(CraftServer.java:172)
	at org.bukkit.craftbukkit.CraftServer.enablePlugins(CraftServer.java:155)
	at net.minecraft.server.MinecraftServer.e(MinecraftServer.java:297)
	at net.minecraft.server.MinecraftServer.a(MinecraftServer.java:284)
	at net.minecraft.server.MinecraftServer.init(MinecraftServer.java:152)
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:348)
	at net.minecraft.server.ThreadServerApplication.run(SourceFile:417)