Yes, it's a member of the main dialog class, CFLModManager. I don't see how the first case would be possible; the second case might, I guess, but I just have one other thread, and it just communicates using SendMessage to the main thread's window. I'll try changing it to PostMessage (not sure if that'll do anything), and increasing a couple buffers that aren't CString's (I doubt they're overflowing, but just to be sure). What makes this crash so hard to debug is that I can't duplicate the crash, and it rarely happens to my users; ~1 crash a week (auto-reported) out of 10,000+ downloads. Fortunately, because it's so rare, it won't be that big of deal if I can't fix it; I don't think it's happened to the same person more than once.