http://forums.polyloop.net/attachment.php?attachmentid=13732&d=1153109813

I was admiring this really incredible render by HowieFarkes (MAN! Carrara can do some really amazing landscapes in the right hands!) and a suggestion was made to increase his SWAP file to 4 GB (see link) to try and fix a similiar sounding problem...

http://forums.polyloop.net/showthread.php?t=8338

Personally, I would never attempt to render something that big- If you use Photoshop you can REZ-UP smaller files without losing hardly ANY noticable sharpness or details for purposes of large format printing. I have two wide format Epson's and do this all the time for art prints...