Index was out of range. Must be non-negative and less than the size of the collection. Parameter name: index gridview

Question

My grid has only one row (always) based on unique condition in database. When I try to edit using Rowcommand am getting error as

"Index was out of range"

Here is grid code and asp.net code:

protected void grdedittemplate_RowCommand(object sender, GridViewCommandEventArgs e) {
    if (e.CommandName == "Update") {
        int index = e.commandargument;
        Label L0 = (Label) grd.Rows[index].Cells[0].Controls[1];
        value.Text = L0.Text;
        Label L1 = (Label) grd.Rows[index].Cells[1].Controls[1];
        value1.Text = L1.Text;
        Label L2 = (Label) grd.Rows[index].Cells[2].Controls[1];
        value2.Text = L2.Text;
        Label L3 = (Label) grd.Rows[index].Cells[3].Controls[1];
        value3.Text = L3.Text;
        Label L4 = (Label) grd.Rows[index].Cells[4].Controls[1];
        value4.Text = L4.Text;
        Label L5 = (Label) grd.Rows[index].Cells[5].Controls[1];
        value5.Text = .text Label L6 = (Label) grd.Rows[index].Cells[6].Controls[1];
        value6.Text = L6.Text;
    }
}