Thanks Ray. I was just looking at an unrelated thing, and something weird seems to have happened to the site (i was only looking at the site in a browser, not changing any files or anything).
But when I log on now, I am just seeing the logo at the top, and blank pages apart from that.
Was it just that one page you changed? I'll download it here and save it as something else, and see if rey-loading the copy I have here fixes that.