Fileout node not rendering out correctly

Im trying to render out a single frame from Shake 4.1, i have tried using jpg, psd and tiff formats but to no avail, and all i get is either a 0kb file, or a small 2kb file of just the bottom of my image (when using psd format). I have played with the globals, and flushed the cashe... and now i am at a loss.
My macbook pro is only a few days old, and am wondering if i'm missing a plug in or something? or if it simply doesn't have enough power, as the node tree is rather large (shk file is about a gig in size....) ... any ideas on how to fix this?
Juneau