So I'm currently trying to get my custom errors to work but when doing so I get the following error:

Server Error in '/' Application.
Runtime Error
Description: An exception occurred while processing your request. Additionally, another exception occurred while executing the custom error page for the first exception. The request has been terminated.

In the event viewer, the only exception happening is the standard database connection error exception but I need to show a custom error page when this happens (even if it's a static html page without using a controller).

This is the custom errors tag in web.config under < system.web >

<customErrors mode="On" redirectMode="ResponseRewrite" defaultRedirect="~/Error">
  <error statusCode="400" redirect="~/Error" />
  <error statusCode="404" redirect="~/Error/NotFound"  />
  <error statusCode="500" redirect="~/Error" />
</customErrors>

Error controller:

using System.Web.Mvc;

namespace Logic.Controllers
{
    public class ErrorController : Controller
    {
        public ViewResult Index()
        {
            return View("Error");
        }
        public ViewResult NotFound()
        {
            return View("NotFound");
        }
    }
}