No mapping exists from object type System.Web.UI.WebControls.Label to a known managed provider native type. Please help!

Question

I am using  a data grid to access and update the data of table in database. I am getting this exception in the update event of the grid.
Please help me find the problem. Any help will be appriciated
feedbk is the dataGrid.


public partial class FeedBackForm : System.Web.UI.Page
    {
        string prefx; string cnum; string email; string SNo;
        String myConnStr = null;
      

        public void dataFillIn()
        {

            myConnStr = ConfigurationSettings.AppSettings["ConnectionString"];
            SqlConnection myConn;
            myConn = new SqlConnection(myConnStr);
            SqlCommand myCommand = new SqlCommand("sp_CLOList", myConn);
            myCommand.CommandType = CommandType.StoredProcedure;
            myCommand.Parameters.AddWithValue("@Prefix", prefx);
            myCommand.Parameters.AddWithValue("@Cno", cnum);
            myCommand.Parameters.AddWithValue("@SecNO", SNo);
            SqlDataAdapter da = new SqlDataAdapter(myCommand);
            DataSet ds = new DataSet();
            myConn.Open();
            da.Fill(ds);
            myCommand.ExecuteNonQuery();
            feedbk.DataSource = ds;
            DataBind();
            myConn.Close();
        }
        protected void Page_Load(object sender, EventArgs e)
        {
            prefx = Request.QueryString["Prefix"];
            cnum = Request.QueryString["Cnumber"];
            email = Request.QueryString["Email"];
            SNo = Request.QueryString["SecNo"];
            this.prefix.Text = prefx;
            this.Cno.Text = cnum;
            this.sec.Text = SNo;
            if (!this.Page.IsPostBack)
            {
                dataFillIn();
                myConnStr = ConfigurationSettings.AppSettings["ConnectionString"];
                SqlConnection myConn;
                myConn = new SqlConnection(myConnStr);
                SqlCommand cmd = new SqlCommand("sp_Feedback", myConn);
                cmd.CommandType = CommandType.StoredProcedure;
                cmd.Parameters.AddWithValue("@Cno", cnum);
                cmd.Parameters.AddWithValue("@Prefix", prefx);
                cmd.Parameters.AddWithValue("@SecNo", SNo);
                myConn.Open();
                fb.Text = cmd.ExecuteScalar().ToString();
                myConn.Close();
            }
        }


 protected void feedbk_UpdateCommand(object source, DataGridCommandEventArgs e)
        {
            string clo = (string)feedbk.DataKeys[e.Item.ItemIndex];
            string Rating = ((TextBox)e.Item.Cells[5].Controls[0]).Text;
            string Criteria = ((TextBox)e.Item.Cells[6].Controls[0]).Text;
            string Justification = ((TextBox)e.Item.Cells[7].Controls[0]).Text;
            myConnStr = ConfigurationSettings.AppSettings["ConnectionString"];
            SqlConnection myConn;
            myConn = new SqlConnection(myConnStr);
            SqlCommand cmd = new SqlCommand("sp_updateCLO", myConn);
            cmd.CommandType = CommandType.StoredProcedure;
            Decimal u = System.Convert.ToDecimal(Rating);
            cmd.Parameters.AddWithValue("@rating", u);
            cmd.Parameters.AddWithValue("@criteria", Criteria);
            cmd.Parameters.AddWithValue("@justification", Justification);
            cmd.Parameters.AddWithValue("@objective", clo);
            cmd.Parameters.AddWithValue("@prefix", prefix);
            cmd.Parameters.AddWithValue("@cnumber", cnum);
            int i = System.Convert.ToInt32(SNo);
            cmd.Parameters.AddWithValue("@snumber", i);
            myConn.Open();
            cmd.ExecuteNonQuery();   (the exception occurs over here)
            myConn.Close();
            feedbk.EditItemIndex = -1;
            dataFillIn();

        }

the stored procedure is
USE [EvalDB]
GO
/****** Object:  StoredProcedure [dbo].[sp_updateCLO]    Script Date: 11/28/2009 16:52:25 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER PROCEDURE  [dbo].[sp_updateCLO]
    @prefix varchar(5), @cnumber varchar(25), @snumber int, @rating decimal(3,2),
    @justification  varchar(255),@criteria varchar(255),@objective varchar(255)
        AS
    Begin

    Update  SectionCLO set Rating=@rating,Justification=@justification,Criteria=@criteria  where Objective=@objective
    and CNumber=@cnumber and CPrefix = @prefix and SNumber =@snumber

end