Thanks 6v6gt for your informative reply and link -very useful, although I consider my board is 'genuine' i.e., a duinoTech V3.0 nano from a reputable Oz dealer, over the counter. The top chip is an Atmel Mega328p, and the bottom chip marked as FDTI FT232RL. The annoying aspect is that it had worked well until the latest WIN update and the drivers all looked to be as specified - they simply won't load ergo the error as quoted in my post. From a software perspective it appears that the latest drivers have a flaw with a missing operator? I am absolutely sure I have done nothing that could have 'fried' the board otherwise. I know programming and connections etc., can be frustrating (I have worked with micro's before) but this is really pushing the boundaries!
It is a clone, but not a forgery. That is, there is no attempt to claim it is a genuine Arduino manufactured product and it is marked with the brand name Duinotech.
However, it could well, as has been said, be built using components which have been forged. If the dealer is reputable, they will have a solution for this if indeed the problem is a fake FTDI chip.
Thanks to those who have contributed to my question. It is still not resolved, so I will continue my search and programming. I am away from home temporarily so I will check the nano out when I get back to my desktop - if no go, I shall replace it with a UNO at least.
Thanks to all those who offered help. However, upon returning home and connecting the nano to my desktop PC, also running WIN 10 Pro 64 (updated), the board worked fine and two ports were visible COM 1 & 3.
It would appear that for some unknown reason my laptop refuses to recognise ports??
(I intend to chase this up with Toshiba).
I trust this info may help others with similar Laptop issues.