We have traced the problem to a rare crash bug caused by having an additional member join the looting of a PvP opponent who had previously not been in any combat since logging on.
Special thanks to Xulos who assisted us in replicating the bug which allowed us to trace it down and eliminate it for good. 25 TC's have been awarded to Xulos.
Computing the probability that at least one of the following events will occur:
P(a or b ... or z) = 1 - P(!a and !b ... and !z)