OK Bryn, can't help you I'm afraid. The only time I've not been able to see polar diagram is when I was testing a beta version of the software that wasn't on general release. The polar diagrams just work, and all you can do is switch it on/off and reset it - that's it.
One last idea, are you running Windows Vista? I've never used Vista but I do know that it can do strange things with files and permissions.
Reading your first post again, are you saying that when you click the polar diagram button, it makes the airfields appear and disappear?