Many people are having problems with the newer XFree86,
I'm using 3.2A, occasionally it dumps out, with no helpful
messages. It's happened less since I went from 2.0.30 to
2.1.38, so it's kind of the reverse...
I assume you're running XFree and not a commercial server,
and I would say the problem really lies with XFree, so
the only real way to fix it for the moment is to get a
commercial server, MetroX is ok, but sluggish here,
personally I've stuck with XFree and just make sure I
use autosaves and such, which is always a good idea anyways.
Sorry I don't have a fix, but going back to a stable X or
getting a commercial one may be the only solution at the moment.
3.1.2 was stable here.
Rik