There I was just offshore on the beach in the Minoan Empire sim, with striking Windlight sky and water settings, and I took the pictures... and tripped over VWR-7672 again.
I guess I was elated at having been in SL for more than an hour without crashing or bringing my computer to its knees, and I forgot. Next time, I'll pull back the resolution. Sigh. I can't ask you to vote for the JIRA entry any more, but could you please watch it? This bug basically kills serious SL photography.
UPDATE: the entry to watch is VWR-24178, which is apparently the real bug; it looks like they're well on the trail to fixing it. *crosses fingers* The workaround for now: if you have "global illumination" enabled, don't make the image size larger than the SL client window.