No value given for one or more required parameters EXCEPTION

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C#

ASP.NET

MS-Access

I have the following code,

It throws an error: No value given for one or more required parameters

but the fields are updated in the update event

 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
                    string scon = @"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";

         OleDbConnection conn = new OleDbConnection(scon);

         try
         {
             OleDbCommand cmd = new OleDbCommand(updateSql, conn);

             cmd.CommandText = updateSql;

             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.ToInt32(quantityThreshold.Text);
             cmd.Parameters.Add("@RateCenterID", OleDbType.Integer).Value = Convert.ToInt32(ratecenterid.Text);

                conn.Open();

                 cmd.ExecuteNonQuery();

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

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

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

Kindly check the code and help me to sort out this task

Regards,
Arjun