Help for an error?

since some days i have this error, but it’s not my plugin, or i don’t see it…
can you help me because my server crash!!
it’s happends after a player logout and login after!!!
[19:23:17] [Server thread/INFO]: Diabl091p lost connection: TextComponent{text=‘Internal server error’, siblings=[], style=Style{hasParent=false, color=null, bold=null, italic=null, underlined=null, obfuscated=null, clickEvent=null, hoverEvent=null, insertion=null}}
[19:23:17] [Server thread/ERROR]: Encountered an unexpected exception
java.lang.NoSuchFieldError: worldObj
at net.minecraft.entity.player.EntityPlayer.func_70999_a( ~[ahd.class:?]
at net.minecraft.entity.player.EntityPlayerMP.func_70999_a( ~[qw.class:?]
at net.minecraft.entity.player.EntityPlayerMP.func_71123_m( ~[qw.class:?]
at ~[rj.class:?]
at ~[gr.class:?]
at ~[rc.class:?]
at net.minecraft.server.MinecraftServer.func_71190_q( ~[MinecraftServer.class:?]
at net.minecraft.server.dedicated.DedicatedServer.func_71190_q( ~[po.class:?]
at net.minecraft.server.MinecraftServer.func_71217_p( ~[MinecraftServer.class:?]
at [MinecraftServer.class:?]
at [?:1.8.0_60]


There was a thread with this last week

I need to get @mumfrey or someone who knows how to fix it ASAP.