Thank you Mike for your help,
from this list it appears that:
1 – the skratch disk fragmentation could be relevant (the total fragmentation indicated by Windows is since this disk is 14% and the files fragmentation is 29 % )
2 – I am not using any antivirus but I have a software named Win Patrol Scotty which is supposed to detect the entrance of BHO into my browsers.
I shall defragment my scratch disk and remove Win Patrol from the list of programs loaded at startup.
I shall let you inform of the results. I think that I had read some months ago a post related to difficulties doing Export to Tape with Canon HV20 or HV10 camcorders but I can’t find it.