Constant crashing when rendering or exporting.

I have a 1:40 (one-hour, 40-minute) project (HD/1080) that keeps crashing when I render...or exporting. I even tried going to File>Project Settings>General>Video Rendering and Playback>Renderer...and selected "Mercury Playback Engine Software Only"...and it still crashes.
The last time i tried this, all was going well for about 40-minutes; other times, it crashed in about a minute. I've attached screen-shot of the type of error message I keep getting.