Using Response.Redirect in MVC action

Question

I have an action method in a controller class as shown below and based on a if condition, system should redirect to MVC page. But, Response.Redirect is not working as expected and throws an exception "Cannot redirect after HTTP headers have been set".

[HttpGet]
        public ActionResult GoToPage(string pageName)
        {
            var path = GetPagePath(pageName.Trim());

            if (!string.IsNullOrWhiteSpace(path))
            {
               // framing the fully qualified path
                path = string.Format("{0}/{1}", ConfigurationFactory.GetConfigurationProvider().GetAppBaseUrl(), path);

                if (!path.ToLower().Contains(".aspx"))
                {
                   Response.Redirect(path));    error line
                }
                return Redirect(path);
            }
            else
            {
                return RedirectToAction("AccessDenied", "Error", new { area = "" });
            }
        }

Can someone help on this?