You definitely should get oodles more RAM.
Having 4 gigs and that many cores is starving the system.
You should have 2GB/core, ideally (16GB, if you can afford to do so).
Until then, you may want to limit AE to using 2 cores.
For the time being, disable "render multiple frames simultaneously" until you can install more RAM.
Check out Crucial for some great RAM deals.
Thank you for the response.
We thought 4GB would be ok after reading this from the CS4 online PDF:
The operating system imposes certain limits on the amount of memory that an application can use. After Effects on the Mac OS X operating system can use up to 3.5 GB of RAM, although only about 3 GB is actually available to the foreground application, because Mac OS X uses approximately 500 MB to load the user interface libraries.
Any single process on OS X can use up to 3.5 GB, but with the "render multiple frames simultaneously" option (i.e. multiprocessing) enabled, you're effectively launching multiple instances of AE, each of which can use the 3.5 GB ceiling (per process).
Also consider the overhead that the operating system requires (~ 1 GB these days), and any other applications/background processes you may have running (i.e. Photoshop, Word, etc...).
4 GB disappears very rapidly.
Also, AE is a RAM intensive application. The more RAM you have, the longer your RAM previews can be (at higher resolutions as well).
Until my extra RAM comes in, any thoughts on how to tweek it get a project out?
I've got a user with a project that just refuses to export. Quicktime errors every time. We've tried exporting as WMV and MOV but neither is working. We've tried using the render queue and the less recommended file > export - neither works. I get errors like 'Quicktime export failed (4)' and 'Quicktime export failed - bad parameter (-50)'
Don't use File > Export > Quicktime.
With 4GB, the background instances used for MP rendering will starve from lack of memory.
Set Memory and multiprocessing to leave 6 CPUs free (yep), so that AE can use the 4 GBs for the main app and 2 background instances. That should work well for most projects. If you still get problems, turn off Multiprocessing when using that project, so that the main app can use as much RAM as possible.