title: Error CS0234 in VS 2015 with build+intelliSense selected
body: <p>When I open my mvc project (mvc5) with razor helper file in app_code folder, the compile was successful but in error list I have the error  below:</p>
  
  <p>Severity Code Description Project File Line Suppression State
  Error CS0234 The type or namespace name 'global_asax' does not exist in the namespace 'ASP' (are you missing an assembly reference?) </p>
  
  <p>The error only appear when the option "Build + IntelliSense" was selected, if I select "Build Only" the error won't show.</p>
  
  <p>Can someone explain why this error occurs and how to eliminate this error? is this a bug in VS2015 since this issue does not occur in vs2013? should I be concerned with this error?</p>
  
  <p>bty the error points to the code below</p>
  
  <pre><code>public RazorHelper() {
  }
  
  protected static ASP.global_asax ApplicationInstance {
      get {
          return ((ASP.global_asax)(Context.ApplicationInstance));
      }
  }
  </code></pre>