I'm running Mac Pro 4,1, OS 10.6.8, 2.66 quad core. I have an SSD as my system disk, and two 500 Gb HDD striped as my media disk. Footage is AVCHD, 1080p 24p from a Canon C100. Any time I leave Premiere, for instance to check e-mail or look something up on the web (which I do often because I'm new to Adobe, I'm transitioning from FCP), when I return to Premiere nothing plays back, either the sequence or a clip in the source monitor. Other functions seem to work, I can still edit, just can't play anything. I have to quit and restart, which fixes it, but that's a very inconvenient problem.
Moved from Cloud forum to Premiere Pro forum where you'll probably get a better response from PP users