passing values from one form to next with Session

See more:

C#

ASP.NET

hi,
i am trying to insert id value passing from previous page to current page but it's giving null exception.
my code is as follow:
.cs file:

protected void btnAdd_Click(object sender, EventArgs e)
   {
       if (objTimberDetails.Insert(Convert.ToInt64(Session["Carting_Challan_ID"].ToString()),
                                   Convert.ToInt32(ddlSpecies.SelectedValue),
                                   txtJungle_no.Text.Trim(),
                                   Convert.ToDouble(txtcoupe_length),
                                   Convert.ToDouble(txtcoupe_girth),
                                   Convert.ToDouble(txtcoupe_cubicmeter),
                                   txtDepot_No.Text.Trim(),
                                   Convert.ToDouble(txtDepot_length),
                                   Convert.ToDouble(txtDepot_girth),
                                   Convert.ToDouble(txtDepot_cubicmeter),
                                   Convert.ToDouble(txtDifference_cubicmeter),
                                   Convert.ToInt32(Session["OfficeID"].ToString())))
       {
           lblStatus.Text = Resources.Language.Common_Record_Add;
       }
       BindGrid(Session["Language"].ToString());

business
logic file:

public clsTimberDetails()
       {
       }
       public bool Insert(long Carting_Challan_ID,
                          int Species_Id,
                          string Jungle_no,
                          double coupe_length,
                          double coupe_girth,
                          double coupe_cubic_meter,
                          string Depot_No,
                          double Depot_length,
                          double Depot_girth,
                          double Depot_cubicmeter,
                          double Difference_cubicmeter,
                          int DIV_ID)
       {
           bool res = false;
           System.Collections.ArrayList sel = new System.Collections.ArrayList();

           sel.Add("SP_trn_TimberD_Insert");
           ArrayList lstParam = new System.Collections.ArrayList();

           SqlParameter param;

           param = new SqlParameter();
           param.ParameterName = "@Carting_Challan_ID";
           param.SqlDbType = SqlDbType.BigInt;
           param.Value = Carting_Challan_ID;
           lstParam.Add(param);


           param = new SqlParameter();
           param.ParameterName = "@Species_Id";
           param.SqlDbType = SqlDbType.Int;
           param.Value = Species_Id;
           lstParam.Add(param);

           param = new SqlParameter();
           param.ParameterName = "@Jungle_no";
           param.SqlDbType = SqlDbType.NVarChar;
           param.Value = Jungle_no;
           lstParam.Add(param);

           param = new SqlParameter();
           param.ParameterName = "@coupe_length";
           param.SqlDbType = SqlDbType.Float;
           param.Value = coupe_length;
           lstParam.Add(param);


           param = new SqlParameter();
           param.ParameterName = "@coupe_girth";
           param.SqlDbType = SqlDbType.Float;
           param.Value = coupe_girth;
           lstParam.Add(param);

           param = new SqlParameter();
           param.ParameterName = "@coupe_cubic_meter";
           param.SqlDbType = SqlDbType.Float;
           param.Value = coupe_cubic_meter;
           lstParam.Add(param);


           param = new SqlParameter();
           param.ParameterName = "@Depot_No";
           param.SqlDbType = SqlDbType.NVarChar;
           param.Value = Depot_No;
           lstParam.Add(param);

           param = new SqlParameter();
           param.ParameterName = "@Depot_length";
           param.SqlDbType = SqlDbType.Float;
           param.Value = Depot_length;
           lstParam.Add(param);

           param = new SqlParameter();
           param.ParameterName = "@Depot_girth";
           param.SqlDbType = SqlDbType.Float;
           param.Value = Depot_girth;
           lstParam.Add(param);

           param = new SqlParameter();
           param.ParameterName = "@Depot_cubicmeter";
           param.SqlDbType = SqlDbType.Float;
           param.Value = Depot_cubicmeter;
           lstParam.Add(param);

           param = new SqlParameter();
           param.ParameterName = "@Difference_cubicmeter";
           param.SqlDbType = SqlDbType.Float;
           param.Value = Difference_cubicmeter;
           lstParam.Add(param);


           param = new SqlParameter();
           param.ParameterName = "@DIV_ID";
           param.SqlDbType = SqlDbType.Int;
           param.Value = DIV_ID;
           lstParam.Add(param);

           res = new eAuctionDAL.SQLDAL().UpdateTransData(sel, lstParam, false);
           return res;

       }

in my sql table i have one more field which is this table's ID which is auto incremented field

what is wrong in this code
pls help.


thanks