Error in C#.net class library code

Can you tell me what is wrong with this code?

In an exisitng C#.net 2008 desktop application, I want to setup a class .cs file so I can do security checks against the active directory. I want to add this code to a project file that contains lots of common routines all the other processing modules use. The code is the following:

using System;
using System.Reflection;
using System.Runtime.Remoting;
using System.IO;
using System.Threading;
using System.Windows.Forms;
using System.Security.Principal;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace En.Common
{
class ActiveDirectory

{

AppDomain.CurrentDomain.SetPrincipalPolicy(PrincipalPolicy.WindowsPrincipal);
//Thread.CurrentPrincipal = new WindowsPrincipal(WindowsIdentity.GetCurrent());
//if ((!Thread.CurrentPrincipal.IsInRole("testit")))

}

}


I want to start with 3 lines of code listed so far. However, the statement,

AppDomain.CurrentDomain.SetPrincipalPolicy(PrincipalPolicy.WindowsPrincipal);

However I am getting the following two errors on this statement:

Error 94 Invalid token '(' in class, struct, or interface member declaration

Error 95 Invalid token ')' in class, struct, or interface member declaration
what is wrong with the code?