Using Response.Redirect in MVC action

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?