C# – Visual Studio 2015, can’t change access modifier of new resources files

I'm trying to create new resources files in VS2015. I created them fine, but when I try to change the "Access Modifier", the dropdown is disabled…

Any ideas?

I'm working in a ASP.NET MVC 6 (ASP.NET5). The project is a Class Library, but I have tested in Web Project with same results.

Thanks!!

Edit: Added Properties window