ShowWindow won't work as expected....

Hi,

I have a little (understanding) problem.

I launch a app with "WinExec(PCHAR(<path to my app>),sw_hide);"
This works fine.
Then I want to app to show and for that I use ShowWindow like:
"ShowWindow(appHwnd, SW_SHOW);"
Doing this, that Taskbar show the application, but the applications form
stays invisible.
WHY???

If I launch a app with "WinExec(PCHAR(<path to my app>),sw_normal);"
I can do
"ShowWindow(appHwnd, SW_HIDE);"
"ShowWindow(appHwnd, SW_SHOW);"
and every thing works fine.

Thanks for hints and help
Rainer