This is a weird issue, but I'm able to recreate it. I've got 3 macbook pros and a mac pro all rendering scenes with materials that are set as compositing backgrounds and frontal mapping on them. The second any machine's display goes to sleep, it renders all frames following with black materials instead of the frontal ones.
I'm using QT prores for the materials. Turning the display settings to "never" for going to sleep solves the problem. This happens regardless of which project or which video file I use as the material.
Any ideas would be appreciated.
I had the exact same issue with R12 using QT movies (.mov).
If anyone is still having this problem, I solved it by converting the movies to TIFF sequences using Adobe Media Encoder.
Then I replaced the .mov in the C4D material with the sequence and voila!