Thanks for your replies, my prob has been solved. I needed to apply 'Persistent' profile association in Logitech Profiler! All works fine now.
I don't like Vista for a number of reasons. UAC being one of them.
I might try Pinnacle, although Logitech Profiler generally works OK and is free.
Interestingly, I worked my prob out myself. I got no precise answer from Logitech support or in this forum, although all response is sincerely appreciated.