northumbria61

Many thanks for tip, and many apologies for not replying sooner!! I had not checked if there were any further postings for some time on assumption that everyone who wished to post had. However I tried your tip - it didn't work!! Maybe I misunderstood you, but I have two options for taskbar icons; one is to start the programme and the other is to unpin the icon from the taskbar. So what I did was to 'click' on qw.exe in its directory and change the icon there, then create a shortcut, which sent it to the desktop, and I then transferred it to the taskbar. With this method you have to insert 'qw.exe' when you have it on the desktop!! A bit fiddily I admit, but nice to have the usual icon back, and - more importantly - the programme working nice and smoothly!
So many thanks northumbria61 for giving me the push to keep trying. And also to everyone else who has posted here, hopefully it is not just myself who has benefited from the adice that has been given here.