Help! Server randomly crashes and d/c's all players.

I Am running Windows 7 64-bit with 4gb of ram. This can occur at any time, ususally with only 3 people online.

Code:

13:54:32 [SEVERE] java.lang.NullPointerException
13:54:32 [SEVERE]      at net.minecraft.server.NetServerHandler.sendPacket(NetS
erverHandler.java:723)
13:54:32 [SEVERE]      at net.minecraft.server.EntityTrackerEntry.updatePlayer(
EntityTrackerEntry.java:235)
13:54:32 [SEVERE]      at net.minecraft.server.EntityTracker.updatePlayers(Enti
tyTracker.java:146)
13:54:32 [SEVERE]      at net.minecraft.server.MinecraftServer.w(MinecraftServe
r.java:556)
13:54:32 [SEVERE]      at net.minecraft.server.MinecraftServer.run(MinecraftSer
ver.java:449)
13:54:32 [SEVERE]      at net.minecraft.server.ThreadServerApplication.run(Sour
ceFile:492)
13:54:32 [SEVERE] Unexpected exception
java.lang.NullPointerException
        at net.minecraft.server.NetServerHandler.sendPacket(NetServerHandler.jav
a:723)
        at net.minecraft.server.EntityTrackerEntry.updatePlayer(EntityTrackerEnt
ry.java:235)
        at net.minecraft.server.EntityTracker.updatePlayers(EntityTracker.java:1
46)
        at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:556)
        at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:449)
        at net.minecraft.server.ThreadServerApplication.run(SourceFile:492)
13:56:56 [INFO] Read timed out
13:57:46 [INFO] Read timed out
14:02:17 [INFO] Connection reset

I am running the following plugins - all updated and working:

Anticheat
AntiRelog
Chestshop
DispenserRefill
dynmap
Dynmap-Factions
dynmap-mobs
Essentials
Factions
GroupManager
HiddenCommandsSigns
SimpleCommandSigns
iConomy
Lockette
MobArena
Multiverse-Core
Multiverse-Portals
OtherDrops
PluginMetrics
SimpleSpleef (Not newest, one revision down)
WorldEdit
WorldGaurd



Before this error people are talking and such. After it has happened, the /list command shows all the players that were online before the error. If anyone tries to connect it errors, and denies the connection. All console commands work fine.

Running Craftbukkit-1.2.5-R1.2



Thanks for any help you can give.