Delphi-PRAXiS - Delphi Service monitoring

I need to know what happening with specified service at runtime to take actions when it state is changed (stopped, deleted, etc.). I tried, but without success, here is what I have:

Delphi-Quellcode:

			procedure SvcNotifyCallback(pvParameter: Pointer);

begin

end;

procedure TForm1.FormCreate(Sender: TObject);

var

  hSvcMan, hSvc: Cardinal;

  Buffer: PSERVICE_NOTIFY;

begin

  hSvcMan := OpenSCManager(nil, nil, SC_MANAGER_CONNECT);

  GetMem(Buffer, SizeOf(PSERVICE_NOTIFYW));

  Buffer^.dwVersion := SERVICE_NOTIFY_STATUS_CHANGE;

  Buffer^.pfnNotifyCallback := @SvcNotifyCallback;

  Buffer.pContext := Pointer(nil);

  hSvc := OpenService(hSvcMan, 'UPS', SC_MANAGER_CONNECT);

  NotifyServiceStatusChange(hSvc, SERVICE_NOTIFY_CREATED or SERVICE_NOTIFY_DELETED, Buffer);

end;

This raises external exception. How to trace service, please?