I am having trouble adding a new Sonar scan to an existing map project. Drag and drop is the only way I have been able to pull tracks into the project.

When I drag a new track into an existing project it doesn't integrate into the map, it just shows the red track.

If I create a bew map and drag all tracks in then the new track maps.

What am I doing wrong?

It depends which project window you drag the track into: if you drag into the layers window (i.e. the finished map), then the track is added as a polyline layer and simply becomes a component of the finished map. If you drag into the "tracks and boundaries" window then the track becomes a data source for map generation. You can also use right-click on the track in the track list on the left and choose the "add to project" option.