Map is "too large" ?

I try to install a OSM map of the Island Milos in Greece
I loaded this map with MapSetToolkit so that it is visiable in Garmin BaseCamp.
From BaseCamo I try to load the map to Garmin Etrex HCx with MapInstall.
After the last “Okay” I get a strange error message :

The map is approximately 1.23 MB, but only 1.89 GB is available in the destination.
Please select fewer maps and try again

Seems small enough for me…

Who has seen this before ?
And how do I solve ?

See and the link to
Search for “Strange Error Message: Not Enough Space” on the latter.