As above, perhaps you have just 'de-selected' City Navigator in the menu?
Try this.
>Press Menu
>Select Settings press OK
>Select Map Info press OK
>Ensure that City Navigator {version X} has a tick against it, if not Press OK
Any luck ?
If not, then are you using Mapsource on the PC ? You'll have to, if you need to send the maps back out to the unit?
More info needed......
V