I just had this issue as well. It seems as if the bundler did not like the extension in the name. Once I removed the extension, the bundler started to work.
You might try doing the following. Notice I've removed the .css
in two places.
Remove the .css
bundles.Add(new StyleBundle("~/content/bundled-styles").Include(
"~/content/flexisel-style.css"));
@Styles.Render("~/content/bundled-styles")