thanks for the links.
Since I made my last post I have been done some mousing around and have found a workaround after checking the log file (Flashinstall.log).
I uninstalled Flash Player, rebooted, installed Mozilla Nightly 10 - which is the 64 bit version of Firefox - and then re installed Flash Player which seems to have fixed my problem.
The problem remains if I use IE9 (32 or 64 bit) and Firefox 7 which I suspect is to do with NPSWF64_11_0_1.dll not being 'associated' with the browsers after a reboot.
Perhaps the same process will fix the issue with Firefox/IE9, but life is short enough as it is and Nightly seems pretty good for now so I'll stick with it.