You haven’t provided enough information to troubleshoot. When you say it “will not open”, exactly what’s happening? Do you get an error message? Does it appear to open but then you can’t see anything? Does nothing happen when you click on the map’s name to select it? Something else?
When I open BaseCamp and select a walk the openstreetmap appears with the walk and waymarks shown.
When I open MapSource and select a walk the walk and waymarks are shown, but against a blank white background. There is no map at all.
If I select Utilities and then Manage Map Products I open a box which shows “OSM generic routable (new style), version 1.00, status not lockable, installed location C;\Garmin\Maps\OSM generic routable (new style). Alongside there are three options. Unlock Online, Copyright and Notice. I can only select copyright, the other two do not respond.