new web page not being reached

In a C# web form 2010 application, I am trying to get an existing web page to point the user to a new page page. The user enters a value into a textbox field and c_textchanged(object sender, EventArgs e) is occurs (is called). When the user is in this routine, I want the application to go to my new web page. However, I am getting the generic error message that occurs is the web site default.

I am trying to do the following command,

command:either   Page.Response.Redirect("Reason.aspx"); or Response.Redirect("~/Reason.aspx");

Thus can you tell me the following:
1. Where in the visual studio.net ide, would I find the real error message? Is there a log file to look at? Where would I find the log file?
2. I am guessing the code can not find the new page. Could there being something wrong with the new page page? This is the only place I am using the partial class called reason. is that a problem?
   The new web page looks like the following:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace Sup.Pages.Proc
{
    public partial class Reason : System.Web.UI.Page
    {

        protected void Page_Load(object sender, EventArgs e)
      }
             }
        }