I haven't explored the problem fully.
Mapsource (I'm using an old version, 6.13, which I prefer to newer versions) 'sees' the E30 OK.
When I go to transfer Waypoints, Routes and Tracks from Mapsource to E30, the Waypoints and Routes are greyed out.
The Tracks appear to transfer OK - little progress bar and everything - but they don't then appear in the E30 menus, even after a restart.
I haven't tried transferring a map, and I haven't tried using Mapsource to import stuff from the E30. Yet.
And I haven't tried a newer version of Mapsource.
I'm happy enough to use the file manager method to do everything, which is why I haven't investigated further.
When I (briefly) had a Dakota, according to the manual, Maspource was the approved method for transferring stuff. And it did work. The E30 manual doesn't mention Mapsource at all. (There is Basecamp of course, which I don't know much about.)