I am having a very similar problem.
I’m running the latest Beta version. I’ll be grading for 15 or 20 minutes, and all of a sudden my clips turn black, and I can’t access them. Only once did it explicitly tell me it was “QTDecoder” but I assume it’s the same problem, because it resulted in the clips all turning black. I am grading PR HQ 444 Slog footage.
I’m running OSX 10.7.4
2.2 i7 8GBs of RAM