export to dwg

I'm having some trouble with saving my drawings to dwg. I have a
macro set up which does it for me, appending a rev letter to the
filename, which I use when I'm ready to send something to a vendor.
The problem I'm seeing is that sometimes after I've exported a
significant number of drawings, it simply stops working. No errors or
anything, I just go to the target directory and there's nothing
there. This also happens when I do a manual save-as.

I'm having another problem which seems related; when I try to output
my overall assembly drawing (1979 parts, 260 unique; 3 ortho views
with broken-out sections, 3 detail views, and an isometric), SW blinks
a lot, clears and redraws the screen very slowly several times
(possibly once for each view; I usually go and do something else while
it's working on this), and then, again, fails to produce a dwg. This
happens even if that drawing is the first file I open after restarting
SW, but afterwards it always reverts to the above behavior.

Anybody seen behavior like this before? Is SW just getting tired and
giving up? Maybe it needs a Red Bull...

SW 2007 SP 4.0, x64, on a dell PWS490 with NV Quadro FX 3500.