Fatal server error, and it's getting worse

Many of my players try logging in, only to have the following message show up in the console:

[WARNING] Failed to handle packet: java.lang.NullPointerException
java.lang.NullPointerException
at net.minecraft.server.ItemStack.a(ItemStack.java:199)
at net.minecraft.server.InventoryPlayer.f(InventoryPlayer.java:104)
at net.minecraft.server.EntityHuman.u(EntityHuman.java:180)
at net.minecraft.server.EntityPlayer.u(EntityPlayer.java:264)
at net.minecraft.server.EntityLiving.o_(EntityLiving.java:231)
at net.minecraft.server.EntityHuman.o_(EntityHuman.java:95)
at net.minecraft.server.EntityPlayer.a(EntityPlayer.java:176)
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:217)
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)

Useful Details-
Windows 7 Home Premium (x86)
Java 7
No wrappers
CraftBukkit 823

An answer on how to fix this or at least a response is very much appreciated. I gotta get this fixed for my players. I want them to be able to enjoy the game without having this error keeping them from playing.

 

Is that the full error log?
What plugins do you have installed?

 

Try downgrading to 818

 

The issue is resolved now. I removed all plugins and everything worked fine. I am adding them back in until I discover which plugin caused the issue. Thanks for your replies everyone!

 

You need to update to craftbukkit #860!

 

look at the dates of each post.

 

And? You'd be surprised how many people don't update to new RB's.

 

Oh it doesn't matter, I thought you were doing a reply to my earlier post.