Good point, thanks. Contacted Garmin here and they acknowledged this problem and are working to solve it.It may but MapInstall only installs the map, not all the other updates that come with a map update that ideally your 595 needs.
You really need to get Express to work, so ensure Express is up to date and try it again.
I have tried the latest Express version but it don't work. I wonder why Garmin have done their system so
that it hide the maps. When I look at the files in my Zumo 595, they are very small, but somewhere is
some big files that take space. I went thru all directories on my Zumo and could not find any big files.
I have to recheck the \.System\SID as Ikraus say.
I asked also it the unit could be total reset and start from empty memory, let's see what they say.