NPE I would like to try narrow down before removing plugins

Happens when some people connect but not others.

PHP:

2011-10-28 18:50:26 [WARNING] Failed to handle packet: java.lang.NullPointerException
java.lang.NullPointerException
at net.minecraft.server.Packet21PickupSpawn.<init>(SourceFile:22)
at net.minecraft.server.EntityTrackerEntry.b(EntityTrackerEntry.java:240)
at net.minecraft.server.EntityTrackerEntry.b(EntityTrackerEntry.java:192)
at net.minecraft.server.EntityTracker.track(EntityTracker.java:33)
at net.minecraft.server.WorldManager.a(WorldManager.java:16)
at net.minecraft.server.World.c(World.java:881)
at net.minecraft.server.WorldServer.c(WorldServer.java:161)
at net.minecraft.server.World.addEntity(World.java:874)
at net.minecraft.server.World.addEntity(World.java:826)
at net.minecraft.server.ServerConfigurationManager.c(ServerConfigurationManager.java:138)
at net.minecraft.server.NetLoginHandler.b(NetLoginHandler.java:121)
at net.minecraft.server.NetLoginHandler.a(NetLoginHandler.java:39)
at net.minecraft.server.NetworkListenThread.a(SourceFile:94)
at net.minecraft.server.MinecraftServer.h(MinecraftServer.java:471)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:374)
at net.minecraft.server.ThreadServerApplication.run(SourceFile:417)
2011-10-28 18:50:26 [SEVERE] java.lang.[NullPointerException]
2011-10-28 18:50:26 [SEVERE] at net.minecraft.server.Packet21PickupSpawn.<init>(SourceFile:22)
2011-10-28 18:50:26 [SEVERE] at net.minecraft.server.EntityTrackerEntry.b(EntityTrackerEntry.java:240)
2011-10-28 18:50:26 [SEVERE] at net.minecraft.server.EntityTrackerEntry.b(EntityTrackerEntry.java:192)
2011-10-28 18:50:26 [SEVERE] at net.minecraft.server.EntityTrackerEntry.scanPlayers(EntityTrackerEntry.java:233)
2011-10-28 18:50:26 [SEVERE] at net.minecraft.server.EntityTrackerEntry.track(EntityTrackerEntry.java:59)
2011-10-28 18:50:26 [SEVERE] at net.minecraft.server.EntityTracker.updatePlayers(EntityTracker.java:118)
2011-10-28 18:50:26 [SEVERE] at net.minecraft.server.MinecraftServer.h(MinecraftServer.java:476)
2011-10-28 18:50:26 [SEVERE] at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:374)
2011-10-28 18:50:26 [SEVERE] at net.minecraft.server.ThreadServerApplication.run(SourceFile:417)
2011-10-28 18:50:26 [SEVERE] Unexpected exception
java.lang.NullPointerException
at net.minecraft.server.Packet21PickupSpawn.<init>(SourceFile:22)
at net.minecraft.server.EntityTrackerEntry.b(EntityTrackerEntry.java:240)
at net.minecraft.server.EntityTrackerEntry.b(EntityTrackerEntry.java:192)
at net.minecraft.server.EntityTrackerEntry.scanPlayers(EntityTrackerEntry.java:233)
at net.minecraft.server.EntityTrackerEntry.track(EntityTrackerEntry.java:59)
at net.minecraft.server.EntityTracker.updatePlayers(EntityTracker.java:118)
at net.minecraft.server.MinecraftServer.h(MinecraftServer.java:476)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:374)
at net.minecraft.server.ThreadServerApplication.run(SourceFile:417)