Fixed: A route named 'umbraco-surface-BaseRoute' is already in the route collection

Chances are you've landed on this pagr from Google after searching for the reason why your newly upgraded Umbraco project (also more than likely upgraded via NuGet) is displaying this wonderful error... 'A route named 'umbraco-surface-BaseRoute'.

Long story sort, it's probably because you've renamed your project and when you compile/run it, Visual Studio created another DLL under the new name for your project, so now you're running with two DLLs that do the same thing. Hence the error. Delete the old DLL and your site will pop back into life.