title: Lyx 2.1 RC1, warning message "the selected document class Article" requires external files
body: <p>I just installed  2.1 RC1 bundle on windows 7</p>
  
  <p>Each time I try to save a document (also when I first open Lyx), I get this message</p>
  
  <p><img src="https://i.stack.imgur.com/UD3O5.png" alt="enter image description here"></p>
  
  <p>LyX-210RC1-Bundle-1.exe </p>
  
  <p>why this happens? Do I need to configure something else? I had Lyx 2.0 before, but I uninstalled that before installing Lyx 2.1</p>