I’ve posted this more for my own reference so I don’t forget it again. Entity Framework refused to add a migration and I did a lot of things to try and get around the error below

System.Data.Entity.Core.ProviderIncompatibleException: An error occurred accessing the database. This usually means that the connection to the database failed. Check that the connection string is correct and that the appropriate DbContext constructor is being used to specify it or find it in the application’s config file. See http://go.microsoft.com/fwlink/?LinkId=386386 for information on DbContext and connections. See the inner exception for details of the failure. —> System.Data.Entity.Core.ProviderIncompatibleException: The provider did not return a ProviderManifestToken string. —> System.ArgumentException: Could not determine storage version; a valid storage connection or a version hint is required.

I eventually discovered the issue was caused by the Start Up project in Visual Studio not being set to the project I was trying to run the Entity Framework migration against. Basically to get around this right click on the project in Visual Studio and select “Set as startup project” then run your migration again and like magic all should work.