my mob arena stopped working

2012-06-03 17:57:40 [SEVERE] Error occurred while enabling MobArena v0.94.4.52 (Is it up to date?)
java.lang.IllegalArgumentException: Block must be a sign!
	at com.garbagemule.MobArena.leaderboards.Leaderboard.<init>(Leaderboard.java:64)
	at com.garbagemule.MobArena.ArenaImpl.<init>(ArenaImpl.java:123)
	at com.garbagemule.MobArena.ArenaMasterImpl.loadArena(ArenaMasterImpl.java:506)
	at com.garbagemule.MobArena.ArenaMasterImpl.loadArenas(ArenaMasterImpl.java:476)
	at com.garbagemule.MobArena.ArenaMasterImpl.initialize(ArenaMasterImpl.java:234)
	at com.garbagemule.MobArena.MobArena.onEnable(MobArena.java:81)
	at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:215)
	at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:337)
	at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:381)
	at org.bukkit.craftbukkit.CraftServer.loadPlugin(CraftServer.java:256)
	at org.bukkit.craftbukkit.CraftServer.enablePlugins(CraftServer.java:238)
	at net.minecraft.server.MinecraftServer.t(MinecraftServer.java:381)
	at net.minecraft.server.MinecraftServer.a(MinecraftServer.java:368)
	at net.minecraft.server.MinecraftServer.init(MinecraftServer.java:197)
	at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:432)
	at net.minecraft.server.ThreadServerApplication.run(SourceFile:492)