I had a problem with my Bus Stop render where I would let my Mac render all night and only had like 20 frames done in the morning. As Robcat pointed out, the machine was set to sleep after a half hour! I had *assumed* that with a render running, the machine would keep cranking, but no, it was going to sleep on schedule. Could it be something like that?
Oh and nice work, Chris! It really is a professional job!