yesterday, for the second time in six weeks or so, Navigator suddenly claimed "No map installed", and, as on the first occasion, a look inside the data directory showed that the file for my regional map was still there, but only with a size of 128 kB. (Luckily, I had a recent back up of my device's complete data - all yesterday I could not acess your map server, eithe via 3g or via WiFi).
Is this a recognised problem, or was I simply unusually unlucky?