Hmmmm... Are you sure you're using the right program to send them to the GPS? I seem to recall there being a couple of different options on the Mac... I'm not sure any more which was the correct one.
No I'm not sure. For the mac there is Road Trip, Base map, Map installer, training centre, etc....
Base map only works with DEM data, so that leaves road trip as the most likely candidate, it certainly displays the maps well, and allows one to transfer routes and waypoints.
There isn't a lot of documentation with these programs, or maybe I am just particularly confused today and I am missing something obvious.