keeps currupting

Hi there. I have a brand new mac book pro with lepoard lastest version and from what i gather you still cant shoot tethered using a P20 and latest 3 version of Capture One Pro. So i am forced to use my old ibook which is a 1.33ghz with 512ram. prob is when i do after about an hour or so of shooting all files come through major curupt, lots of black and colured banding, lots of spare memory and not getting hot....just does it...and every time. Any help would be great.

Matt