Hi Bruce, I disabled add-ons one by one,after installing the update, but it made no difference. I also flushed the DNS cache and that made no difference.I then ran sfc /scannow and errors were found (I don't know what they were) and successfully repaired.I also rebooted my modem and router. Finally (famous last words) IE9 is working properly.

Thanks to you and everyone else who contributed to this thread.

Regards,Roy