frame buffer problem

i'm having an issue with after effects that i can't figure out. i have a big project that has many precomps. one of them is very large (5000x5000) and within it is a solid that is even bigger. i understand that after effects has a certain limit for how big a canvas can be but this shouldn't be pushing the limits (i've done bigger before). especially given the equipment i'm working on. i just got the lastest mac pro with terabytes of hard drive space and 16GB of physical ram. i tried rendering this as a movie file but quickly came to the conclusion that an image sequence would work better (and would help me pick up where my render failures left off). i've adjusted all of my memory and cache settings to allow for the maximum available space for AE to use but it still fails when it comes to the area with the large comp and solid. the really weird part is that the frames that crash the image sequence render will render out if you render them out individually (save as file). i just don't understand that. why would it render the frame individually but fail when rendering the image sequence? anyway, i know there are companies, post houses that do bigger projects that this. i hope there is a solution that i'm overlooking. i've already gone the route of breaking the project into pieces but i don't think that's the issue because this part still fails even when everything else is turned off. i'm using AE CS3 (intel) on mac os 10.5.3, quicktime 7.5. there is a boris continuum complete plugin on the layer but even when it's turned off, it fails (it's the latest boris version). sometimes ae gives me the error of frame buffer size problems and sometimes it fails without error messages.

any suggestions will be very appreciated. i'm at my wits end with this.

thanks