add new row in gridview using session

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VB

ASP.NET

I have a grid, which is already populated from database. I am inserting a new row in grid from a popup window using session variable. Now, problem is when i insert second time a new row in grid, first one disappears.
How can i solve this problem.

Here's my code, which i am using for above functionality. What change can i made to resolve my problem.

Dim con1 As New SqlConnection(ConfigurationManager.ConnectionStrings("MyConnectionString").ConnectionString)
       con1.Open()
       Dim ada1 As New SqlDataAdapter("P_FN_PR_PopGrid", con1)
       Dim ds1 As New DataSet
       Try
           ada1.SelectCommand.CommandType = CommandType.StoredProcedure
           ada1.SelectCommand.Parameters.Add(New SqlParameter("@date", SqlDbType.DateTime)).Direction = ParameterDirection.Input
           ada1.SelectCommand.Parameters("@date").Value = Trim(RadDatePick.SelectedDate.Value)
           ada1.SelectCommand.Parameters.Add(New SqlParameter("@sc", SqlDbType.Char)).Direction = ParameterDirection.Input
           ada1.SelectCommand.Parameters("@sc").Value = Trim(ddlSc.SelectedValue)
           ada1.SelectCommand.Parameters.Add(New SqlParameter("@me", SqlDbType.Char)).Direction = ParameterDirection.Input
           ada1.SelectCommand.Parameters("@me").Value = Trim(ddlme.SelectedValue)
           ada1.Fill(ds1, "P_FN_PR_PopGrid")
           ada1.Dispose()
           If (Not IsNothing(Session("NewRec"))) Then
               Dim lst As List(Of Rec) = TryCast(Session("NewRec"), List(Of Rec))
               For Each rec As Rec In lst
                   Dim rw As DataRow = ds1.Tables(0).NewRow()
                   rw("port_rec_num") = rec.port_rec_num
                   rw("DESC_ALT") = rec.DESC_ALT
                   rw("port_no_se") = rec.port_no_se
                   rw("STD_NUM_OF_SE") = rec.STD_NUM_OF_SE
                   ds1.Tables(0).Rows.InsertAt(rw, 0)
                   Next
           End If
           GD_Prod.DataSource = ds1.Tables(0).DefaultView
           GD_Prod.DataBind()
       Catch Err As Exception
           Response.Write(Err.Message.ToString)
       Finally
           con1.Close()
       End Try
       Session.Remove("NewRec")
   End Sub