Gridview update(not functioning)

string updateSql = "UPDATE RateCenters SET RateCenterName = @RateCenterName, Province= 
@Province, QuantityThreshold = @QuantityThreshold" + "WHERE RateCenterID= @RateCenterID";


    protected void GridView1_RowUpdating(object sender, GridViewUpdateEventArgs e)
    {                    
        GridViewRow row = (GridViewRow)GridView1.Rows[e.RowIndex];

        DropDownList ddl = (DropDownList)row.FindControl("DropDownList2"); // assigning the dropdownlist item to 'ddl'

        TextBox rateCenterName = (TextBox)row.FindControl("txtRateCenterName"); // assigning textbox input item

        TextBox quantityThreshold = (TextBox)row.FindControl("txtQuantityThreshold"); // assigning textbox input item

        Label ratecenterid = (Label)row.FindControl("Label1"); // assigning the label value

     //  OleDbConnection conn = new OleDbConnection(ConfigurationManager.ConnectionStrings["DBConnection"].ToString());

        OleDbConnection conn = new OleDbConnection(@"Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\Documents and Settings\arjun.giridhar\My Documents\Visual Studio 2010\Projects\BillingApplicationNew\BillingApplicationNew\App_Data\db1.mdb;Persist Security Info=False");

        OleDbCommand cmd = null;

        try
        {


            cmd = new OleDbCommand(updateSql, conn);


            cmd.Parameters.Add("RateCenterName", OleDbType.VarChar).Value = rateCenterName.Text;
            cmd.Parameters.Add("Province", OleDbType.VarChar).Value = ddl.SelectedItem.Text;
            cmd.Parameters.Add("QuantityThreshold", OleDbType.Integer).Value = Convert.ToUInt32(quantityThreshold.Text);
            cmd.Parameters.Add("RateCenterID", OleDbType.Integer).Value = Convert.ToInt32(ratecenterid.Text);


            conn.Open();
            cmd.Connection = conn;
            cmd.ExecuteNonQuery();

            //GridView1.EditIndex = -1; //refreshing
            //GridView1.DataBind();
        }

        catch (OleDbException ex)
        {
            throw (ex);
        }

        finally
        {

            conn.Close();
            conn.Dispose();
        }
    }