Lyman, I seem to recall that the WRG / ACARS meaning was under significant discussion in either the first or second (or both?) AF 447 thread.
After knocking about for a while ... this made some sense to me ...
http://www.pprune.org/tech-log/39510...ml#post6392828
" ... the difference between ACARS 'WRN' and 'WRG' : it doesn't reference interconnection failure for the latter, just a mistrust."
Lupine translation renders "mistrust" as a sign that two things speaking electricity to each other are having a "WTF?" or "say again?" moment.
And of interest to ACARS fans
AF447 ACARS MESSAGES - Color Coded & Interactive Version