datagridview lostfocus fire when click on cells of DGV

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C#

It's a strange thing.
There is a DGV in my form which user can add rows to it.but when I click on a cell Of
First row to add some data it is disable and I can't enter anything.
I disabled all event except datagridview_LostFocus and I found the problem is this.
But I don't know how!!!!in this event I try to activate another control in form when
DGV lost focus(for example by Tab key)

void dataGridView1_LostFocus(object sender, EventArgs e)
{
  if (chkbxChange.Enabled == false)
    lblPrsnlCod.Focus();
}