Thanks for replying. That's fine as long as there's nothing to worry about. It just struck me as odd that there'd be this error after playing when opening the gamelist. Like I say I didn't see it on the last release and thought it worth mentioning, but if you're saying it's all good, that's good enough for me. :-)
FWIW the scraping for this particular system was done some time ago via Skraper and I'd been manually editing it to trim the collection down to something more suited to the Pi. I thought it was my error at first but noticed the same thing on other systems I wasn't manually editing.
Anyway not to worry, thanks again.