Error in closing another application...

I tried to open Norton Anti Virus using ShellExecute.
After a few seconds, I tried to close it using SendMessage as below.
But it didn't work. I've done the declaration for the WM_CLOSE and all
the Windows API but still didn't work. Before this, I used PostMessage but
still not working. The return value was 0.
Can anyone guide me? Any other method of closing another application effectively?
Maybe an example or two will be greatly appreaciated... Thanks..

'##################################################################'
'***'in module
Public Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long

Public Declare Function ShellExecute Lib "shell32.dll" Alias "ShellExecuteA" (ByVal hWnd As Long, ByVal lpOperation As String, ByVal lpFile As String, ByVal lpParameters As String, ByVal lpDirectory As String, ByVal nShowCmd As Long) As Long

Public Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long

Public Declare Function GetActiveWindow Lib "user32" () As Long
Public Declare Sub Sleep Lib "kernel32" (ByVal dwMilliseconds As Long)

Public Const WM_CLOSE = &H10
Public Const WM_DESTROY = &H2

'***'in form

Dim retval As Long
Dim hWnd2 As Long

hWnd2 = GetActiveWindow
retval = ShellExecute(hWnd2, "open", "C:\Program Files\Norton SystemWorks\Norton AntiVirus\navw32.exe", "c:\myTemp.txt", 0&, SW_MINIMIZE)
Debug.Print "ShellExecute = " & retval

Sleep 12000

hWnd2 = FindWindow(vbNullString, "Norton AntiVirus")
Debug.Print "findwindow = " & hWnd2

z = SendMessage(hWnd2, WM_CLOSE, 0, 0 )
Debug.Print "z = " & z
z = SendMessage(hWnd2, WM_DESTROY, 0, 0)
Debug.Print "z = " & z
'####################################################################

WM_CLOSE has the same effect as clicking the close icon (X). Does Norton Anti Virus normaly quit if you click that icon?

There are other ways (but that's not how you should do it) like
TerminateProcess(handle,returncode)

Thanks a lot for ur opinion.. I think I found out the reason behind this.. There is another Norton running in the background - NortonAntiVirusAutoProtect.. So, each time I send the WM_CLOSE message, it will close the background process and not the Norton Window that I just opened...
Thanks a lot, anyway...

:)

For future reference, when closing an running application I would suggest using PostMessage rather than SendMessage. SendMessage function sends the specified message to a window or windows. The function calls the window procedure for the specified window and does not return until the window procedure has processed the message. The PostMessage function, in contrast, posts a message to a thread’s message queue and returns immediately. As a result, PostMessage will react to your request much more quickly.