Thanks, Derek.
The difference is that the other thread is, as far as I understand, referring to capture or transfer from the camera to computer.
I have already captured this stuff from a Firestore FS-C over the past 5 months. It is only now, after changing my settings for the last few days to do a ProRes job, that I come back to this and find that the files are unreadable.
However, I've been messing around and I find that these wretched HDV files are perfectly readable when I boot from a LEOPARD (not Snow Leopard) drive.
It is only under Snow Leopard that I now can't open them.
I have, as I said, reinstalled Snow Leopard, Trashed Prefs, reinstalled FCP 6.0.6, run Disk Warrior and Disk Utility. I have also made sure that I am running ProApps 5.1 and not Pro Apps 6, which completely messes up my FCP.
This is sudden and weird. If you have any bright ideas - however outlandish - please let me know and I will come to your house in order to be your eternal slave.
Thanks for the reply.
Best
Harry.