我需要插入例外细节到sql server数据库

我的问题是我有一个aspx页面，它在其代码文件中有尝试和捕获块，它将在catch中使用异常对象处理异常，现在当程序执行达到这个捕获块时，它调用公共方法GetExceptionDetails，它将返回一个长字符串文本，其中包含异常的所有属性的值，但不是属性的名称。现在，当我将属性值插入数据库的表对象字段时，一切都是正确的，直到代码到达db.submitchanges()时，其中弹出一条异常语句，读取sqldatetimeoverflow和sqltypesexception。请帮我找出这个问题，下面是整个代码:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
namespace WebApplication5
{
    public partial class EnterMarks : System.Web.UI.Page
    {
        public float average,total;
       public string grade,chk,exmessage;
        DataClasses1DataContext db = new DataClasses1DataContext();
        protected void Page_Load(object sender, EventArgs e)
        {   
            if (Request.QueryString["StudentID"] != null)
            {
                Label1.Text = Request.QueryString["StudentID"];
            }
        }
        protected void Button1_Click(object sender, EventArgs e)
        {
            List<int> stdID = new List<int>();
            tblGrade tb = new tblGrade();
            total = (float)(Convert.ToDouble(TextBox1.Text) + Convert.ToDouble(TextBox2.Text) + Convert.ToDouble(TextBox3.Text));
            average = total / 3;
            if (average > 85 && average < 90)
            {
                grade = "AA";
            }
            else if(average>80 && average<85)
            {
                grade = "A";
            }
            else if (average > 75 && average < 80)
            {
                grade = "BB";
            }
            else if (average > 70 && average < 75)
            {
                grade = "B";
            }
            else if (average > 65 && average < 70)
            {
                grade = "C";
            }
            else if (average > 60 && average < 65)
            {
                grade = "CC";
            }
            else if (average > 55 && average < 60)
            {
                grade = "D";
            }
            else
            {
                grade = "DD";
            }
            //var query = from m in db.tblGrades
            //            where m.StudentID == Convert.ToInt32(Request.QueryString["StudentID"])
            //            select m;
            // foreach (var q in query)
            //{
                tb.StudentID = Convert.ToInt32(Request.QueryString["StudentID"]);
                tb.Grade = grade;
                db.tblGrades.InsertOnSubmit(tb);
                db.SubmitChanges();
            Response.Redirect("WebForm1.aspx");
        }
        protected void Button2_Click(object sender, EventArgs e)
         {
            //var query1 = from n in db.tblContacts where n.StudentID == int.Parse(TextBox4.Text) select n;
             tblExcDet te = new tblExcDet();
            var query1 = from n in db.tblContacts select n.StudentID;
            //try
            //{

                foreach (var q in query1)
                {
                    if (q.Equals((int.Parse(TextBox4.Text))))
                    {
                        Label2.Text = "ID Found";
                    }
                }
                try
                {

                    int? i = null;
                    tblContact tc = new tblContact();
                    tc.StudentID = (int)i ;
                    //db.tblContacts.InsertOnSubmit(tc);
                    db.SubmitChanges();
                }
                catch (Exception ex)
                {
                    exmessage = GetExceptionDetails(ex);
                    te.ExMessage = exmessage.Split('*')[0];
                    te.ExData = exmessage.Split('*')[1];
                    te.ExInner = exmessage.Split('*')[2];
                    te.ExTargetSite = exmessage.Split('*')[3];
                    te.ExStackTrace = exmessage.Split('*')[4];
                    te.ExHelplink = exmessage.Split('*')[5];
                    te.ExSource = exmessage.Split('*')[6];
                    te.ExHresult = exmessage.Split('*')[7];
                    db.tblExcDets.InsertOnSubmit(te);
                    db.SubmitChanges();
                    Label2.Text = "Can't assign null value into a table id";
                }



        }
        //public static string GetExceptionDetails(Exception ex) 
        //{
        //    var properties = ex.GetType().GetProperties();
        //    var fields  = properties.Select(property=>new{
        //        name = property.Name,value = property.GetValue(ex,null)
        //    }).Select(x => String.Format(
        //                 "{0} = {1}",
        //                 x.name,
        //                 x.value != null ? x.value.ToString() : String.Empty
        //             ));
        //    return String.Join("*", fields);
        //}
        public static string GetExceptionDetails(Exception ex)
        {
            var properties = ex.GetType().GetProperties();
            var fields = properties.Select(property => new
            {
                name = property.Name,
                value = property.GetValue(ex, null)
            }).Select(x => String.Format(
                         "{0}",
                         x.value != null ? x.value.ToString() : String.Empty
                     ));
            return String.Join("*", fields);
        }
    }
}

 context.Log = Console.Out;

SqlDbType.DateTime