[eluser]Wayne Smallman[/eluser]
OK, I've just confirmed what I'd suspected, and that the error I'm getting appears only to be happening with Chrome.
Also, this isn't a new installation of CodeIgniter; the project is months old.
As I said, this error only started recently, which I now think is somehow linked to me using Chrome (version 6.0.472.63 on Mac OS X 10.6.4).