Is this NUI or
 

is this LUA Error from NUI or another addon

Message: Interface\FrameXML\ChatFrame.lua:3946: attempt to perform arithmetic on a nil value
Time: 12/06/11 16:26:08
Count: 1
Stack: Interface\FrameXML\ChatFrame.lua:3946: in function `ChatEdit_UpdateHeader'
Interface\FrameXML\ChatFrame.lua:3671: in function `ChatEdit_ResetChatType'
Interface\FrameXML\ChatFrame.lua:3743: in function <Interface\FrameXML\ChatFrame.lua:3727>
Interface\FrameXML\ChatFrame.lua:3753: in function `ChatEdit_DeactivateChat'
Interface\FrameXML\InterfaceOptionsPanels.lua:978: in function `InterfaceOptionsSocialPanelChatStyle_SetChatStyle'
Interface\FrameXML\InterfaceOptionsPanels.lua:907: in function <Interface\FrameXML\InterfaceOptionsPanels.lua:894>

Locals: editBox = ChatFrame2EditBox {
0 = <userdata>
headerSuffix = ChatFrame2EditBoxHeaderSuffix {
}
focusLeft = ChatFrame2EditBoxFocusLeft {
}
focusRight = ChatFrame2EditBoxFocusRight {
}
chatFrame = ChatFrame2 {
}
addSpaceToAutoComplete = true
tabCompleteTableIndex = 1
focusMid = ChatFrame2EditBoxFocusMid {
}
header = ChatFrame2EditBoxHeader {
}
}
type = "SAY"
info = <table> {
sticky = 1
flashTabOnGeneral = false
flashTab = false
}
header = ChatFrame2EditBoxHeader {
0 = <userdata>
}
headerSuffix = ChatFrame2EditBoxHeaderSuffix {
0 = <userdata>
}
(*temporary) = nil
(*temporary) = nil
(*temporary) = ChatFrame2EditBoxHeader {
0 = <userdata>
}
(*temporary) = nil
(*temporary) = "SAY"
(*temporary) = "_SEND"
(*temporary) = nil
(*temporary) = nil
(*temporary) = "attempt to perform arithmetic on a nil value"

List of addons
NUI
NUI Config Chat frames
NUI config GUI
skada
DBM
Bloodshield

Doesn't look like nUI. Most if not all of the nUI modules begin with "nui". Jus in case, disable the "NUI Config Chat frames" addon and see if it goes away

The error itself is within blizzards chatframe system and it doesn't directly link into where the area came from to give us a clue as to whether something was passed to it from an addon or it was a number generated off the fly.

I wouldn't be surprised though if it is a side affect of addons playing with the chatframes. I get the error once in a blue moon and usually on a character I haven't played too recently but haven't been able to track down the culprit.

I see this error, too, from time to time... I *think* it is a side effect of me messing with the chat frames in nUI but I have yet to have found the actual culprit.

It's on the to-do list... which might take me a bit to get caught up and to-done.