Have you tried starting Word in Safe Mode (i.e. hold down the Ctrl key while starting Word)?

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]

Thanks for the reply.
I tried that but Word didn't start (it's 2007, by the way). I have no active addins but is there anything else that Safe Mode would prevent from loading?
What does work is if I start Word then open the document but that defeats the benefit of being able to click on the document directly.
Is there any significance in the fact that the problem went away after renaming the Normal template (even though it came back on the next document load)?

That suggests there is some other application interfering with the way Word should work. You previously said
In that case, you might try going off-line, then disabling McAfee and re-testing your system. If Word then runs correctly, either in Safe mode or normally, McAfee is indeed the likely culprit.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]

Good suggestion. I did that but the message appeared.
Do you have any view on why renaming Normal.dotm worked (if only once)?

If your application works when normal.dotm is renamed and does not work with the original, the problem is in that file.

There are lots of things that can happen to any file, including the normal template. When you rename it, Word works from its defaults and may create a new normal template.

Here is more about the Normal Template.