using System;
using System.Diagnostics;

public class ProcessTest
{
	public static void Main(string[] args)
	{
		Process p = new Process();
		p.StartInfo.FileName = "ls";
		p.PriorityClass = ProcessPriorityClass.Normal;
		p.Start();
	}
}

Unhandled Exception: System.ComponentModel.Win32Exception: Some sort of w32 error occurred: 6
  at System.Diagnostics.Process.set_PriorityClass (ProcessPriorityClass value) [0x00000]
  at (wrapper remoting-invoke-with-check) System.Diagnostics.Process:set_PriorityClass (System.Diagnostics.ProcessPriorityClass)
  at ProcessTest.Main (System.String[] args) [0x00000]