bstrapper.cs

  pipelines.OnError += (ctx, exception) =>
            {
                ctx.Items.Add("OnErrorException", exception);
                return null;
            };

errorstatuscodehandler.cs

public class ErrorStatusCodeHandler : IStatusCodeHandler
    {
        private readonly IResponseNegotiator responseNegotiator;

        public ErrorStatusCodeHandler(IResponseNegotiator responseNegotiator)
        {
            this.responseNegotiator = responseNegotiator;
        }

        public bool HandlesStatusCode(HttpStatusCode statusCode, NancyContext context)
        {
            return statusCode == HttpStatusCode.InternalServerError;
        }

        public void Handle(HttpStatusCode statusCode, NancyContext context)
        {
            var response = new Negotiator(context);

            Error error = null;
            if (context.Items.ContainsKey("OnErrorException"))
            {
                var exception = context.Items["OnErrorException"] as Exception;
                error = new Error { ErrorMessage = exception.Message, FullException = exception.ToString() };
            }

            response.WithModel(new ErrorPageViewModel
            {
                Title = "Sorry, something went wrong",
                Summary = error == null ? "An unexpected error occurred." : error.ErrorMessage,
                Details = error == null ? null : error.FullException 
            }).WithStatusCode(statusCode).WithView("Error");

            var errorresponse = responseNegotiator.NegotiateResponse(response, context);
            context.Response = errorresponse;
        }
    }