I have a COM application for managing WinAPI. Everything worked well for 2K, XP and even vista when suddenly I faced such a problem: the "Next" button in hardware installation dialog is not always clicked by my application.

-It is always clicked if I use my PressButton method twice although.
-Buttons are clicked in apps like Calculator etc..
-My QA engineer says that messages are sent to right handles=)
-My PressButton methods simply sends WM_LBUTTONDOWN/LBUTTONUP to handle of button control.
-If send "Alt+N", the button is clicked.
-Before we try to click, focus is set to "InstallationPath" ComboBox.