There are more reports that MapSource 6.14.1 has changed in such a way that it breaks most OSM map installers, not only for Germany. It will take some time for the maintainers to get things working again. In the mean time I suggest you stick with an older version of MapSource…
I had the same problem, however the supplied registry file suggests that the map folder (OSM-Germany?) should reside in C:\Garmin (have you put it there?). So either copy that folder there or change the registry settings to where it is now. That worked for me.