How do I display custom error pages in Asp.Net Mvc 3?

I want all 401 errors to be be redirected to a custom error page. I have initially setup the following entry in my web.config.

<customErrors defaultRedirect="ErrorPage.aspx" mode="On">
  <error statusCode="401" redirect="~/Views/Shared/AccessDenied.aspx" />
</customErrors>

When using IIS Express I receive the stock IIS Express 401 error page.

In the event when I do not use IIS Express a blank page is returned. Using Google Chrome's Network tab to inspect the response, I see that while the page is blank a 401 status is returned in the headers

What I have tried thus far is using suggestions from this SO answer since I am using IIS Express but to no avail. I have tried using a combination <custom errors> and <httpErrors> with no luck - the standard error or blank page is still displayed.

The httpErrors section looks like this at the moment based on the link from the above SO question ( I also found another very promising answer however no luck - blank response)

<system.webServer>
  <httpErrors  errorMode="DetailedLocalOnly" existingResponse="PassThrough" >
    <remove statusCode="401"  />
    <error statusCode="401" path="/Views/Shared/AccessDenied.htm" />
  </httpErrors>

 <!-- 
 <httpErrors  errorMode="Custom" 
             existingResponse="PassThrough" 
             defaultResponseMode="ExecuteURL">
      <remove statusCode="401"  />
  <error statusCode="401" path="~/Views/Shared/AccessDenied.htm" 
         responseMode="File" />
 </httpErrors>
 -->
</system.webServer>

I have even modified the applicationhost.config file and modified <httpErrors lockAttributes="allowAbsolutePathsWhenDelegated,defaultPath"> to <httpErrors lockAttributes="allowAbsolutePathsWhenDelegated"> based on information from iis.net. During the course of my endeavours I also managed to stumbled upon this error as described in another SO question.

How do I display custom error pages in Asp.Net Mvc 3?

Additional info

The following controller actions have been decorated with the Authorize attribute for a specific user.

[HttpGet]
[Authorize(Users = "domain\\userXYZ")]
public ActionResult Edit() 
{
   return GetSettings();
}

[HttpPost]
[Authorize(Users = "domain\\userXYZ")]
public ActionResult Edit(ConfigurationModel model, IList<Shift> shifts)
{
    var temp = model;
    model.ConfiguredShifts = shifts;
    EsgConsole config = new EsgConsole();

    config.UpdateConfiguration(model.ToDictionary());
    return RedirectToAction("Index");
}