What steps will reproduce the problem?
1. Happened once in an unusual circumstance, so reproducing is going to be tough. Basically, in a 10-man raid party at VoA. Some people are inside, some are outside. No trash has been engaged and have not reached the bosses yet. At the summoning stone outside, an error was thrown up. One member of the party may or may not have been engaged in a dual with another person at the time of the error.

What is the expected output? What do you see instead?
Instead of no problems: the error.

What version of the product are you using?
r153

Do you have an error log of what happened?
    ["message"] = "EnsidiaFails-r153\\EnsidiaFails.lua:1471 attempt to index field '?' (a nil value)\n\nLocals:|r\nSometimes debuglocals() returns nothing, it's one of those times... (FYI: This message is a HotFix from Decursive to prevent a C stack overflow)\n  ---",
            ["type"] = "error",
            ["session"] = 2190,
            ["counter"] = 1,
        }, -- [909]

Please provide any additional information below.
USEnglish client/server, WoW 3.2.2.10505 live.