Unable to update the data from gridview control ?

See more:

VB

ASP.NET

Here is the code to update the perticular field of the gridview

Protected Sub UpdateTDetails(ByVal sender As Object, ByVal e As GridViewUpdateEventArgs)
      Try


      Dim LblID As Integer = DirectCast(GridViewTDetalis.Rows(e.RowIndex).FindControl("lblID"), Label).Text
      Dim txtfuncobj As String = DirectCast(GridViewTDetalis.FooterRow.FindControl("txtfuncobj0"), TextBox).Text
      Dim txtmeasuredvar As String = DirectCast(GridViewTDetalis.FooterRow.FindControl("txtmeasuredvar0"), TextBox).Text
      Dim txtdeadline As String = DirectCast(GridViewTDetalis.FooterRow.FindControl("txtdeadline0"), TextBox).Text
      Dim txtweight_fact As String = DirectCast(GridViewTDetalis.FooterRow.FindControl("txtweight_fact0"), TextBox).Text

      Dim con As New SqlConnection(strConnString)
      Dim cmd As New SqlCommand()
      cmd.CommandType = CommandType.Text
      cmd.CommandText = "update MBO_Details set MBO_FUNC_OBJ=@func_obj,MBO_MEASURED_VAR=@mesrd_var,MBO_DEADLINE=@tar_dt,MBO_WEIGHT_FACT=@wt_fact where id=@idnum;" _
      & "select id, MBO_EMP_CODE,MBO_FUNC_OBJ, MBO_MEASURED_VAR, MBO_DEADLINE,MBO_WEIGHT_FACT from MBO_Details where MBO_EMP_CODE='40000001'" 'where emp_no='" & (EMP_NO) & "' and trid is null  order by id"

      cmd.Parameters.Add("@idnum", SqlDbType.VarChar).Value = LblID
      cmd.Parameters.Add("@func_obj", SqlDbType.VarChar).Value = txtfuncobj
      cmd.Parameters.Add("@mesrd_var", SqlDbType.VarChar).Value = txtmeasuredvar
      cmd.Parameters.Add("@tar_dt", SqlDbType.VarChar).Value = txtdeadline
      cmd.Parameters.Add("@wt_fact", SqlDbType.VarChar).Value = txtweight_fact

      GridViewTDetalis.EditIndex = -1
      GridViewTDetalis.DataSource = GetDataTDetails(cmd)
          GridViewTDetalis.DataBind()
      Catch ex As Exception
          MsgBox(ex.Message)
      End Try
  End Sub

but gets the error message
"Object reference not set to an instance of an object."
what will the problem ?