Restrict Users to Launching Only One Instance of an Application

static void Main() 
{
	Process ThisProcess = Process.GetCurrentProcess();

	Process [] AllProcesses = Process.GetProcessesByName(ThisProcess.ProcessName);

	if (AllProcesses.Length > 1)
	{
		MessageBox.Show(ThisProcess.ProcessName + " is already running",
ThisProcess.ProcessName, MessageBoxButtons.OK, MessageBoxIcon.Error);
	}
	else
	{
		Application.Run(new MainForm());
	}
}