I'm not sure what changed that caused this to be a problem for me. When I try to do a remakefw on my machine, I get a compile error on SimpleRootSite saying that INotifyCollectionChanged is defined multiple times. It is defined in System.dll and in WindowsBase.dll. The WindowsBase.dll is a .NET assembly and SimpleRootSite is using an older version of this assembly (.NET 3) for some reason. In .NET 4, this interface was moved from WindowsBase.dll to System.dll. When I ignore this warning, the remakefw works.