Curl Error 6 : Could Not Resolve Host on Windows Universal

In the unity editor, I load an image from a URL. This works fine in the editor for preview.

 private IEnumerator LoadFromCoroutine()
     {
         WWW wwwLoader = new WWW(url);
         yield return wwwLoader;
         RenderSettings.skybox.mainTexture = wwwLoader.texture;
     }

When I execute after I compile it for windows universal, I get this error:

Curl Error 6 : Could Not Resolve Host on Windows Universal

Any clues?