Releasing window handle

I am working on testing a file copy application. I created a tiny win32 console app to help with testing. This app has to just set focus on a window named "Copy File" and exit. Then I manually click on Cancel to cancel copy or OK to continue copying.

Here is the code:

HWND anyWindow = ::FindWindow(NULL,"Copy File");

:: SetForegroundWindow(anyWindow);

anyWindow = NULL;

Once the app bring the copy file app to forground, I click cancel and exit. Then I try to delete the file I am trying to copy. But I cannot delete the file because I get an error saying I can proceed with the delete. If I do this manually, it works fine. But if I use my test app, I get the error message. I suspect that my test app is holding on to the copy file window handle even after it exits. Is setting anyWindow window handle to NULL the right way to release the handle?