Have you recently done a map update or been tinkering around on the internal memory with the GPS plugged into a PC?
On the 660 all the mapping should be on the internal memory, if you had a 550 it could be down to having the mapping on an SD card.
As said above, assuming that you have a myGarmin account with the Zumo registered and you bought it within the last 12 months then you should be able to retrieve the mapping as an update. Go
here and follow the instructions.
If you have a fully unlocked version of the mapping on your PC in Mapsource you could also recreate your mapping data from there. To check if it is fully unlocked find the unlock code in your myGarmin account and then, in Mapsource (assuming a recent version), click 'Utlities' > 'Manage Map Products' and click the 'Unlock Regions' tab. Now double click the mapping version you have, or had, on your Zumo. This should show the unlock code that should match that in your myGarmin account. If it does then you can create a new mapping data file from your own PC.
In Mapsource zoom out to 500 miles so you can see all of Europe. Select the map tile tool an drag across the whole map until your select everything. This should give you 372 map tiles at 2.22GB (City Nav 2012.2, other versions may well vary) in the Maps pane on the left. Now plug in a USB stick with at least that much space free. Now click the send to device icon and select the memory stick, ensure that the Maps checkbox only is ticked. Now click send. This could take a few hours to build the index files depending on your PC. Watch TV or go to bed...
Once complete you will have file named 'gmapsupp.img' in a folder, called 'garmin', on your memory stick as well as a .gma file with a series of numbers in front of it.
You now need to back-up the following files from the 'garmin' folder on the internal memory of your GPS to the hard drive of your PC; 'gmapprom.img' and 'gmapprom.gma'. Once you've done this rename the files you created from Mapsource which are now on your memory stick and transfer them to the 'garmin' folder on the GPS.
Now unplug the GPS from the PC let it boot up, now reboot the Zumo by switching it off and on again and pray...
The above method will only update your mapping data, 3D data and probably junction view might no longer be operational depending on if these files were also corrupted.
If you can do it any other way then go for that...
