Cannot set scoreboard for invalid CraftPlayer

Weird error that doesn't happen on my test server but does on the real server:

Code:

2014-01-22 13:00:17 [WARNING] [AnarchyPlugin] Task #49 for AnarchyPlugin v1.0 generated an exception
java.lang.IllegalStateException: Cannot set scoreboard for invalid CraftPlayer
at org.bukkit.craftbukkit.v1_6_R3.entity.CraftPlayer.setScoreboard(CraftPlayer.java:1016)
at Scoreboard.MainScoreboard.setScoreboard(MainScoreboard.java:221)
at Scoreboard.JoinEvent$2.run(JoinEvent.java:41)
at org.bukkit.craftbukkit.v1_6_R3.scheduler.CraftTask.run(CraftTask.java:58)
at org.bukkit.craftbukkit.v1_6_R3.scheduler.CraftScheduler.mainThreadHeartbeat(CraftScheduler.java:345)
at net.minecraft.server.v1_6_R3.MinecraftServer.t(MinecraftServer.java:530)
at net.minecraft.server.v1_6_R3.DedicatedServer.t(DedicatedServer.java:240)
at net.minecraft.server.v1_6_R3.MinecraftServer.s(MinecraftServer.java:493)
at net.minecraft.server.v1_6_R3.MinecraftServer.run(MinecraftServer.java:425)
at net.minecraft.server.v1_6_R3.ThreadServerApplication.run(SourceFile:583)