They have suggested that I should try a using a windows 64 bit operating system. They say this is the limit of a 32 bit system.

(Apparently, Macs don't have this problem). I have spoken to Graphisoft Australia who tell me that the problem is due to the fact that Windows can only address a maximum of 1.7 Gb of Ram. The CPU capacity would always sit at maximum during the rendering process say 98% so this also convinces me it was not a modelling issue but a hardware issue. The behaviour was inconsistent across different computers using the same file. They would often also produce blank screens instead of renders. The problem was as the file got more and more detailed and complicated through the design process the PC's started to give me more and more errors and eventually crash. I spent 40% of my time trying to get each of the computers to render without error. They turned out well, but I had alot of trouble with the our PC's. I was really interested to see what I could achieve in 2 weeks. I then proceeded to use the Lightworks package to render large perspectives for a competition that week.

I recently went to the Lightworks in Archicad seminar, which was very informative (Thankyou Dwight!).

Lightworks 32 bit