I use I.E. It has focus but shift to other control I guess that it capture the "Tab" key while I press "Alt-Tab" to switch back.
Anyway, I write a rountine in DeActivate event to capture last focus. And then, restore it in Activate event. However, I find another problem ... if I press the key quickly, it will force me back since I use Calllater. I need to modify the code. Thanks.

