The problem is now fixed but I do not understand why. Although the widget wouls not work when viewed from my instance of IE9, it did not affect another PC running the same version. I could not see anything in the console window.
I went through settings one by one with no success until I clicked Reset Advanced Settings and then the widget worked fine. However, by doing this I’ve lost any means of finding out which settings affected the widget. This would have been useful in the event that other users of my site (www.sagasonline.org) encountered problems.
It is a great plug-in – many thanks.