For my workflow, I'm rendering flv files from AE CS6 and then importing that file onto my stage/timeline in Flash CS6. It crashes about every other time, enough to make it a pattern. No other Flash files give me this problem, eg those without the flv file imported. Even when I reopen the file with an embedded flv file, it will crash about every other time.
The flvs aren't that long, ranging from 50-150 frames. Usually no audio.