Here you go. Same issue - list the Name as me, not sa (I use sa instead of
administrator for our domain admin username).

using System;
using System.Runtime.InteropServices;
using System.Security.Principal;
using System.Threading;

namespace TestImpersonate
{
    class Program
    {
        [DllImport("advapi32.dll", SetLastError = true)]
        public static extern bool LogonUser(String lpszUsername, String
lpszDomain, String lpszPassword,
            int dwLogonType, int dwLogonProvider, ref IntPtr phToken);
        [DllImport("kernel32.dll", CharSet = CharSet.Auto)]
        public extern static bool CloseHandle(IntPtr handle);

        const int LOGON32_PROVIDER_DEFAULT = 0;
        const int LOGON32_LOGON_NETWORK = 3;

        static void Main(string[] args)
        {
            string username = "sa";
            string password = "*****";

            AppDomain.CurrentDomain.SetPrincipalPolicy(PrincipalPolicy.WindowsPrincipal);
            string domainName = Thread.CurrentPrincipal.Identity.Name;
            domainName = domainName.Substring(0, domainName.IndexOf('\\'));

            IntPtr tokenHandle = new IntPtr(0);
            bool returnValue = LogonUser(username, domainName, password,
                                        LOGON32_LOGON_NETWORK, LOGON32_PROVIDER_DEFAULT,
                                        ref tokenHandle);
            if (returnValue == false)
                throw new Exception("Windows logon Error: " +
Marshal.GetLastWin32Error());

            WindowsIdentity identity = new WindowsIdentity(tokenHandle);
            WindowsImpersonationContext impersonationContext = identity.Impersonate();

            IPrincipal prin = Thread.CurrentPrincipal;
            Console.Out.WriteLine("user = " + prin.Identity.Name);

            impersonationContext.Undo();
            impersonationContext.Dispose();
            CloseHandle(tokenHandle);

        }
    }
}