SelectedValue which is invalid because it does not exist in the list of items.

Question

dear please help me to solve below problem....

getting error in fillgird()..

 'cmbcontractor_name' has a SelectedValue which is invalid because it does not exist in the list of items.

Parameter name: value

dear i am sending class file..... 

 public DataTable gridviewfetch()

    {

        

        library lib = new library();

        DataTable dtdetailview = new DataTable();

        dtdetailview = lib.GetconDetail();

        return dtdetailview;

  }

and aspx page fillgrid()...

private void fillgrid()

    {

        DataTable dttab = cons.gridviewfetch();

        {

            if (dttab.Rows.Count > 0)

            {

             GridView1.DataSource = dttab;

             GridView1.DataBind();

            }

            else

            {

                dttab.Rows.Add(dttab.NewRow());

                GridView1.DataSource = dttab;

                GridView1.DataBind();

                int TotalColumns = GridView1.Rows[0].Cells.Count;

                GridView1.Rows[0].Cells.Clear();

                GridView1.Rows[0].Cells.Add(new TableCell());

                GridView1.Rows[0].Cells[0].ColumnSpan = TotalColumns;

                GridView1.Rows[0].Cells[0].Text = "No Record Found";

            }

        }

thanksyou.....