BaseCamp: sending openstreet maps to SD

Hi,
I've downloaded Europe BaseCamp zip file from OpenMapChest.
I unzipped the OpenMapChest Europe.gmap folder into C:\Program Files (86)/Garmin\BaseCamp\Maps

Now I would like to install a subset of the europe map (e.g. Italy + Austria + Switzerland) on my SD card.
BaseCamp 4.7.5 can see the SD card (with empty Garmin folder).

Maps -> Install Maps -> Continue ...

Then I try to selects a part of the Europe map by using left button of the mouse.
Nothing is selected :-(
What I'm doing wrong ?
Thanks, Alessandro