Ever tried to have a TextBox control inside an UpdatePanel fire a TextChanged event? If you can answer Yes to this question, you probably know that the TextBox in question loses it's focus .. and if you've tried TextBox.Focus() you know this does not work inside an UpdatePanel.
The trick is to use the SetFocus(control) method of the ScriptManager on the page instead, e.g.: ScriptManager1.SetFocus(txtAntalLager);