I would guess that you only downloaded the repository settings and the maps for your location while you were still online.

Unless you are tethering to your cell phone for a mobile data connection you need to download the map tiles in advance.

Look in the menu under Maps... Manage Maps...
There you can specify an area to download, but you need to have the Lat/Long coordinates of the Top-Left and Bottom-Right points for the rectangle shaped area for which you wish to download map images.

Personally I took some saved tracks and loaded them as a route and let it download the tiles by route instead of by area.

-r2