I had the same error and I just have 2 Gb RAM. I already increased the max ram-cache and max memory. Well I did a quick research and I followed the instructions at the adobe help center 🙂
https://livedocs.adobe.com/en_US/AfterEffects/8.0/help.html?content=WSF13D6BED-C53B-408a-B2D6-C8B4205D4FB7.html
It says that errors can occur when using higher values than the presets. I also had the external Cache on the same Disk which is not the best option. Hope some of those tipps may help you too! They did in my case.
Tom