Atlanta Region had done a shorter night enduro earlier that year as a test for the ARRC enduro and it ran very smoothly. But it was also held in June (I think) with clear weather.
That year's ARRC got behind schedule fairly early on Saturday due to the rain, so the enduro started at least an hour later than originally planned. That meant the race started in the dark AND rain. Cars started falling off the course and getting stuck on lap 1. Visibility was poor and attempts at full course yellows were difficult at best.
In my opinion (I was a flagger at the time) it was the combination of rain and darkness at the start that doomed the race. Had the race started in daylight, even with rain, I think it would have been okay. Likewise, had it been clear weather all day, even starting in the dark would have probably worked out.
Because there were so many problems, it's unlikely to be done again. Also, the current schedule of sprint races on Saturday with the enduro on Sunday seems to work pretty well.