Thanks heaps Lars! Fixed!
Turns out the Gravatar error was the culprit. I’ve disabled avatars for now until the Gravatar people address the bug (I suppose).
Anyway, no Gravatars is not a big worry for me as I don’t have active subscribers yet on this site.
Re: the upgrade, I did download the code on the download tab Lars but I wasn’t confident the version was 4.5. Which file would indicate that to me?