Invalid LatLonBox error when importing georeferenced KML or KMZ maps from GoogleEarth into Basecamp

I GeoReferenced images of two maps in Google Earth (Idaho Area and Laos Target Echo):
Download for KML and KMZ (these are not routes - they are entire maps):
When I import any of these files into Basecamp I get the error message:
GroundOverlay : [name of map] Invalid LatLonBox
The georeferenced map doesn't appear anywhere in Basecamp.
What am I doing wrong? These same files open back up just fine in GoogleEarth.