FSNav - missing runways

Got a problem with FSNav that has stumped even the author.
The runways in some London airfields have vanished but the surrounding areas and countries seem ok.
Even Helge, the author, is stumped. Any of you seen this and have a fix?
Hopefully there should be a screen dump with this post but I'm about as good at technical stuff as I am a typnig.
[img]URL[/img]http://www.simviation.com/yabbuploads/London.jpg
The runways in some London airfields have vanished but the surrounding areas and countries seem ok.
Even Helge, the author, is stumped. Any of you seen this and have a fix?
Hopefully there should be a screen dump with this post but I'm about as good at technical stuff as I am a typnig.
[img]URL[/img]http://www.simviation.com/yabbuploads/London.jpg