If you have map data 0.2.47.103 (released Dec 2012) installed in your phone and cannot start navigation in Maps v3.06 in offline mode, update the map data with Nokia Suite or via Wi-Fi connection. The issue with offline navigation is fixed in map data 0.2.49.104.
With map data 0.2.47.103 you could get the error below if trying to start navigation in offline mode:
"Car navigation cannot start at this location"