Try to put in a "fresh" copy of SOAR pilots.
Something similar happened to me. I got a message from Windows saying that one of the files in Soar Pilots.pbo is corrupt and/or unreadable, don't remember exactly which it was, and that happened just like that; out of the blue, no abnormal shutdowns etc.
Then Windows went on to advise that I should run Scandisk(Checkdisk-XP)
While it was checking a bunch of delete's took place and when I looked in my addons folder ther was a folder called "bas_soarpilots.pbo". And that was written in green, for which I have no idea what it means; blue text is when you compress, but green? :-\
Now I'm not saying that this will/has happen/ened to you; it just serves as an example of the weird but wonderful yet unstable world of addons.
Btw, do you have a lot of addons (a lot = 1,5 GB+)?
Have fun figuring it out!
Bye
P.S.: And despite the fact that it was in a folder it worked!?