Launching an application from a service

Hi,
I've managed to write a service application.
From within this thread I have to launch an application.
I need to unzip an archive. Unfortunately, using the "classic" scheme of
launching across "ShellExecuteEx" (see code below) the neither SMC nor the
application that is "launched" returns any error or does the job.
So, what can I do?

Any idea is welcomed.

Code:
  FillChar(ExecInfo, SizeOf(ExecInfo), 0);
  with ExecInfo do begin
    cbSize := SizeOf(ExecInfo);
    fMask := SEE_MASK_NOCLOSEPROCESS;
    Wnd := 0;
    lpFile := PChar(lExec);
    lpParameters := PChar(lParam);
    nShow := SW_HIDE;
  end;
  ShellExecuteEx(@ExecInfo);
  RaiseLastOSError;
  try
   WaitForSingleObject(ExecInfo.hProcess, INFINITE);
  finally
   CloseHandle(ExecInfo.hProcess);
  end;
Where:
  lExec = 'Winzip32.exe'
  lParam = ' -min -e -o archive.zip'

Thanks,
Mike_