static void Main()
        {
            bool createdNew;                                    
            Mutex mutex = new Mutex(false, "Single", out createdNew);
        
            if (!createdNew)                                      
            {
                Process currentProcess = Process.GetCurrentProcess();
                foreach (Process process in Process.GetProcessesByName(currentProcess.ProcessName))
                {
                    if ((process.Id != currentProcess.Id) &&
                        (Assembly.GetExecutingAssembly().Location == process.MainModule.FileName))
                    {
                        IntPtr mainFormHandle = process.MainWindowHandle;
                        if (mainFormHandle != IntPtr.Zero)
                        {
                            ShowWindowAsync(mainFormHandle, 1);      
                            SetForegroundWindow(mainFormHandle); 
                        }
                    }
                }
                //MessageBox.Show("进程已经开启");
                return;
            }
            else
            {
                Application.EnableVisualStyles();
                Application.SetCompatibleTextRenderingDefault(false);
                Application.Run(new MainFrame());
                //mutex.ReleaseMutex();       //释放Mutex一次
            }
        }

我这样写，在关闭窗体的时候释放那里会报错：