When calling Win32 functions or handling window messages associated with an application's taskbar button, you must use the global TApplication's window handle (TApplication::Handle).

This window handle is the parent of all the application's forms' handles. Many Win32 functions require window handles that are not that of child windows. FlashWindow is an example of such a function. It can flash the title bar and/or the task bar button of a window. If the window is a child window, then it can only flash the title bar of the window. Supplying Application->Handle for the HWND parameter of FlashWindow will allow flashing of the taskbar.