Thanks Dennis.
Someway I did not pick up on this reply until today so I have not yet tried switching polling OFF yet.
However, I did slow down the polling and that seemed to help a bit but the error was still happening, until this morning!?
When I started my computer today my Eset antivirus software reported the need for a critical update.
When I tried to install that it failed. Help suggested I run a Microsoft Fixit program. Once I did that and restarted the computer the critical update installed OK. And "touch wood" as we say, I have not experienced the program error message in the last 15 minutes or so since.
Another thing I noticed in the available updates list were two for the FTDI device dated in April 2012. I may need to look at those too.
I'll keep an eye on it for now, but hopefully it may be solved.
Thanks
73 de Cliff.....ZL4AS