could not get ardrone_navdata

[boonflies]

When I try to get the navigation info, while running the simulator, as

The navigation info

rostopic echo /ardrone/navdata

I seem to get the following error in the terminal.

ERROR: Cannot load message class for [ardrone_autonomy/Navdata]. Are your messages built?

I am able to get the sonar height information using,
rostopic echo /sonar_height