Stopwatch - missing using directive?

[salmo]

All of a sudden I have a problem with the Stopwatch class. It throws a missing using directive error. I know that this class in held in System.Diagnostics, but when I open that directive the stopwatch is not there.

using System;
using maddox.game;
using maddox.game.world;
using System.Runtime.InteropServices;
using System.Text;
using System.Collections;
using System.Collections.Generic;
using maddox.GP;
using System.Threading;
using System.Diagnostics;

public class Mission : AMission
{
    Stopwatch timer = new System.Diagnostics.Stopwatch();  // missing using directive
    Stopwatch timer = new Stopwatch();  // missing using directive
}

Any ideas what's going on? I've used stopwatch many times before without any problems.