Thanks N, but I'm not sure if it's the same issue. We have never recieved anything as useful as a fatal error, just a page not found. I'm pretty sure it has something to do with our server setup, as the problem re-occurs regardless of which versions of the quiz and moodle we use. Currently using the latest stable build.
I am new to moodle and fairly new to configuring PHP so it's likely I have overlooked something obvious. Its proving very hard to track down the cause since everything else in moodle works perfectly (so far ).