There are a couple of other threads that refer to this problem, but no answers, and apparently replying one of those threads doesn't bring it to the first page, so I'm starting a new thread.
I just upgraded from CS3 to CS4 and now my ram previews are vanishing at the drop of the hat. Something as simple as scrubbing the timeline, which I often like to do with ram previewed footage is causing the preview to completely disappear forcing me to re-render. Its driving me crazy. I've tried adjusting the memory, multiprocessing, disk cache, hardware acceleration settings to no avail.
I'm on an 8 core mac pro with 16Gig ram. AE 9.0.2
My footage includes stills, DVCPro HD footage, and some best quality photo jpeg and animation compressed pre-renders.
I didn't have this problem on CS3, same project same machine.
Unfortunately I have no answers, but I just want to register that I have exactly the same problem. Live Update is on. Multiprocessing on or off makes no difference, I have turned off Open GL... anything I have missed?