Thank you, markshum and ratscloset and Miss Nancy.

For the record, on Mac the preferences are in /Library/Preferences/Poser Pro. I already (effectively) deleted all the preferences by moving these files to a backup location before restarting Poser.

The problem was isolated to Poser Pro. Poser 7 and everything else still worked fine, so I'm sure it was just something that broke within PPro when my render crashed.

Anyway, it's all okay now after a re-install, and I just have to recover all the bits and pieces from my old Runtime. Most of my content is in external libraries anyway, so it's only the scripts and stuff that must be installed in the main runtime.

I could have tried re-installing Poser Pro over the old installation, but it was getting late and I was tired and I just wanted to see it working again so I could sleep easy. How sad is that? :O)

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)