There is an issue where by if you try to connect to a server that try's to create a duplicate objective, as the stack trace calls it (its actually a player on the scoreboard), the client will crash instead of just excepting the new objective.

Although I found this bug in the process of making a bukkit plugin, this is NOT a problem with bukkit, rather a problem with the vanilla handling of the scoreboard.

I'm sure I will find a workaround that will no doubt over-complicate things for me, I think this should really be addressed.

Here is the stack trace:

u: Exception in world tick
at net.minecraft.client.Minecraft.l(SourceFile:1334)
at net.minecraft.client.Minecraft.K(SourceFile:574)
at net.minecraft.client.Minecraft.run(SourceFile:526)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.IllegalArgumentException: An objective with the name 'Citizen' already exists!
at arj.f(SourceFile:163)
at bdl.a(SourceFile:1125)
at fd.a(SourceFile:99)
at ci.b(SourceFile:350)
at bdl.d(SourceFile:95)
at bdt.b(SourceFile:58)
at net.minecraft.client.Minecraft.l(SourceFile:1325)
... 3 more