Forms Data Controls :: Unable To Retrieve A Gridview Selected Row Cells Data

i am still stumped with this operation: i am trying to retrieve a GridView selected row data..here is my code.. the commented part that gives me the selectedindex works just fine....but the one giving the selected row cell value does't work and there is no error.. The update operation is done successfully...weired. i need to assigned selected row cells values to variables ..do some calculations and then re-assign the result calculation to cell[9]..

protected void GridView1_RowUpdating(object sender, GridViewUpdateEventArgs e)
{
string s = GridView1.SelectedRow.Cells[5].Text;
TextBox1.Text = s.ToString();
//string s2 = GridView1.SelectedIndex.ToString();
//TextBox1.Text = s2.ToString();
}