Just read the thread in the link I posted. It explains how you can either downgrade to an earlier version of MapInstall or use Garmin's older Mapsource software.
Garmin screwed up here, but GPSFileDepot is not without fault either. Members here stubbornly used Garmin's old registry-based map format which has a variety of issues and has caused a lot of grief for users over the years. Garmin's newer gmap format avoids all these problems, and I have urged other mapmakers to switch to it for years, with no luck. The recently-revised map-making tutorial on this site still uses the old registry format in fact.
But... "it is what it is". So, you have four options:
1. Purchase a Garmin topo map, which includes tech support and is guarnteed to work
2. Find a third party map that uses the newer gmap format
3. Downgrade to an old version of Basecamp/MapInstall
4. Use Garmin's old Mapsource software.
Most people will probably go for option 3 or 4.