C# MVC - Losing Virtual Directory when using RedirectToRouteResult on session time out

Question

I'm building an MVC 4.5.2 application and am having problems with the virtual path getting lost using RedirectToRouteResult. I've created a SessionTimeout Filter Attribute that checks to see if session variables are expired and consequently redirecting to the "Home" controller and "Index" action. The app is running in a virtual directory say example.com/AppBeta. My Controllers are decorated with the SessionTimeout filter attribute but instead of redirecting to example.com/AppBeta/Home it redirects to example.com/Home once the session is empty, causing a 404 error.

How can I use RedirectToRouteResult without losing my virtual directory path?

    public class SessionTimeoutFilterAttribute : ActionFilterAttribute
    {
        public override void OnActionExecuting(ActionExecutingContext filterContext)
        {
            HttpContext ctx = HttpContext.Current;
            HttpSessionStateBase session = filterContext.HttpContext.Session;

            // If the browser session or authentication session has expired...
            if (session.IsNewSession || ctx.Session["ValidSession"] == null)
            {
                if (filterContext.HttpContext.Request.IsAjaxRequest())
                {
                    // Setting statuscode to internal server error should trigger ajaxError at client
                    filterContext.HttpContext.Response.StatusCode = (int)System.Net.HttpStatusCode.InternalServerError;
                    // in case of response is success at client - inform calling JavaScript code that a user should be redirected.
                    var result = new JsonResult;
                    result.Data = "SessionInternalServerError";
                    result.JsonRequestBehavior = JsonRequestBehavior.AllowGet;
                    filterContext.Result = result;
                    //filterContext.Result = new JsonResult { Data = "SessionInternalServerError" };
                }
                else
                {
                    // For round-trip requests.
                    // Redirect to Home which will redirect to Users or Inventory controller base on role
                    filterContext.Result = new RedirectToRouteResult(
                    new RouteValueDictionary { 
                            { "Controller", "Home" },
                            { "Action", "Index" }
                        });
                }
            }
            base.OnActionExecuting(filterContext);
        }
    }