One of my users keep getting a internal server error. Help?

He says his error is "Internal Server Error" every time he tries to log onto my server.

I get an error message that looks like:
13:49:34 [INFO] HeyItsCj [/216.40.166.99:49213] logged in with entity id 700218
at ([ Windfall] -316.7043460850946, 64.0, -504.31407998190934)
13:49:35 [WARNING] Failed to handle packet: java.lang.NullPointerException
java.lang.NullPointerException
at net.minecraft.server.ItemStack.d(ItemStack.java:95)
at net.minecraft.server.ItemStack.f(ItemStack.java:103)
at net.minecraft.server.InventoryPlayer.canHold(InventoryPlayer.java:126
)
at net.minecraft.server.EntityItem.b(EntityItem.java:130)
at net.minecraft.server.EntityHuman.i(EntityHuman.java:218)
at net.minecraft.server.EntityHuman.u(EntityHuman.java:210)
at net.minecraft.server.EntityPlayer.u(EntityPlayer.java:281)
at net.minecraft.server.EntityLiving.o_(EntityLiving.java:231)
at net.minecraft.server.EntityHuman.o_(EntityHuman.java:96)
at net.minecraft.server.EntityPlayer.a(EntityPlayer.java:197)
at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:286)
at net.minecraft.server.Packet10Flying.a(SourceFile:126)
at net.minecraft.server.NetworkManager.b(NetworkManager.java:226)
at net.minecraft.server.NetServerHandler.a(NetServerHandler.java:75)
at net.minecraft.server.NetworkListenThread.a(SourceFile:105)
at net.minecraft.server.MinecraftServer.h(MinecraftServer.java:399)
at net.minecraft.server.MinecraftServer.run(MinecraftServer.java:309)
at net.minecraft.server.ThreadServerApplication.run(SourceFile:422)

I am using the latest recommended bukkit build on a Windows XP 32-bit OS.

 

Plugins?

 

I believe his inventory may be a bit .. bugged. Might have an invalid item stored in his inventory. I would suggest trying to delete/rename his player file at world/players/HeyItsCj.dat and see if he continues to have an issue afterwards.

 

Did CJ happen to run into a glitched sign?

 

Yes he did. He was the first one to report the sign glitch in fact lol