Hmmm, doesnt sound like it should b overly troublesome. Might be worth trying to export as tiny jpegs to see if it is just running out of memory, because it might be something else.
The problem is, SU cant address more than 4GB of RAM, even if youve got it. So upgrading your RAM wont actually help. Youll need to find a workaround, if the memory is the problem, of course.