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)?