[Inno Setup] 执行程序，返回值不为0时提示用户

procedure LoadPerfCounter();
var
  Ret : Integer;
begin
  if Exec(ExpandConstant('{sys}') + '\lodctr.exe',
         '/m:test.man', ExpandConstant('{app}') ,SW_HIDE, ewWaitUntilTerminated, Ret) then
  begin
    if Ret <>  then
    begin
      MsgBox('Error when loading performance counters.' + ## + SysErrorMessage(Ret), mbError, MB_OK);
    end;
  end;
end;