Yes you are probably right SIW2, I was going by this qoute on one of the sky forums :-
" Drives intended for PVRs are different to those meant for computer use. One of the key differences I believe is error checking. Drives meant for PVRs are more defect tolerant and thus won't skip/jump so much if they encounter a glitch during recording, whereas a drive meant for a pc will be much more fastidious about every bit/byte being accounted for at all times, which can cause problems whilst it phaffs about trying to resolve the error"