If your bundling your scripts and CSS then assets like images may not be found.
In your BundleConfig.cs file, create your bundle with CssRewriteUrlTransform:
bundles.Add(new StyleBundle("~/Content/css/bootstrap").Include("~/Content/bootstrap.min.css", new CssRewriteUrlTransform()));
Include in _Layout.cshtml:
@Styles.Render("~/Content/css/bootstrap")
Everything should be good. And yes, viewing what’s happening over the network to see what URL is generating the 404s will help.
EDIT:
Ensure you are using Microsoft.AspNet.Web.Optimization v1.1.0. Confirmed version 1.1.3 causes this error as well.