设置AD密码的问题

如题，用超级用户设置密码时不会报错，当用普通用户设置时就会报错了，这个应该是权限的问题，但我不知道怎么设置才是对的，希望高人指点。。谢谢，代码如下：
 public bool SetPassword(ADUserInfos adUser)
        {
            bool isSuccess = false;
            try
            {
                DirectoryEntry user = GetUser(adUser.SAMAccountName);                // 模拟超级管理员，以达到有权限修改用户密码
                NtsIdentityImpersonation impersonate = new NtsIdentityImpersonation(AdminName, AdminPassword, LdapDomainName);
                impersonate.BeginImpersonate();                user.Invoke("SetPassword", new object[] { adUser.PassWord });                impersonate.StopImpersonate();                user.Close();
                //user.Invoke("SetPassword", adUser.PassWord);
                //user.CommitChanges();
                isSuccess = true;
            }
            catch
            { }
            return isSuccess;
        } #region
    /// <summary>
    /// 模拟登陆
    /// </summary>
    public class NtsIdentityImpersonation
    {        [DllImport("advapi32.dll", SetLastError = true)]        public static extern bool LogonUser(String lpszUsername, String lpszDomain, String lpszPassword, int dwLogonType, int dwLogonProvider, ref IntPtr phToken);        [DllImport("advapi32.dll", CharSet = CharSet.Auto, SetLastError = true)]        public extern static bool DuplicateToken(IntPtr ExistingTokenHandle, int SECURITY_IMPERSONATION_LEVEL, ref IntPtr DuplicateTokenHandle);        [DllImport("kernel32.dll", CharSet = CharSet.Auto)]        public extern static bool CloseHandle(IntPtr handle);        // 要模拟的用户的用户名、密码、域(机器名)        private String _sImperUsername;        private String _sImperPassword;        private String _sImperDomain;        /// <summary>
        /// 记录模拟上下文
        /// </summary>
        private WindowsImpersonationContext _imperContext;        private IntPtr _adminToken;        private IntPtr _dupeToken;        /// <summary>
        /// 是否已停止模拟
        /// </summary>
        private Boolean _bClosed;
        /// <summary>
        /// 构造函数
        /// </summary>
        /// <param name="impersonationUsername">所要模拟的用户的用户名</param>
        /// <param name="impersonationPassword">所要模拟的用户的密码</param>
        /// <param name="impersonationDomain">所要模拟的用户所在的域</param>        public NtsIdentityImpersonation(String impersonationUsername, String impersonationPassword, String impersonationDomain)
        {            _sImperUsername = impersonationUsername;            _sImperPassword = impersonationPassword;            _sImperDomain = impersonationDomain;            _adminToken = IntPtr.Zero;            _dupeToken = IntPtr.Zero;            _bClosed = true;        }        /// <summary>
        /// 析构函数
        /// </summary>
        ~NtsIdentityImpersonation()
        {            if (!_bClosed)
            {                StopImpersonate();            }        }        /// <summary>
        /// 开始身份角色模拟
        /// </summary>
        /// <returns></returns>
        public Boolean BeginImpersonate()
        {            Boolean bLogined = LogonUser(_sImperUsername, _sImperDomain, _sImperPassword, 2, 0, ref _adminToken);            if (!bLogined)
            {                return false;            }            Boolean bDuped = DuplicateToken(_adminToken, 2, ref _dupeToken);            if (!bDuped)
            {                return false;            }            WindowsIdentity fakeId = new WindowsIdentity(_dupeToken);            _imperContext = fakeId.Impersonate();            _bClosed = false;            return true;        }        /// <summary>
        /// 停止身分角色模拟
        /// </summary>
        public void StopImpersonate()
        {            _imperContext.Undo();            CloseHandle(_dupeToken);            CloseHandle(_adminToken);            _bClosed = true;        }    }
    #endregion public DirectoryEntry GetUser(string sAMAccountName)
        {
            DirectoryEntry temp = null;
            try
            {
                DirectoryEntry entry = new DirectoryEntry(ldapPath + ldapDomain, adminName, adminPassword,AuthenticationTypes.Secure);                DirectorySearcher mySearcher = new DirectorySearcher(entry);                mySearcher.Filter = ("(objectClass=user)");                foreach (SearchResult resEnt in mySearcher.FindAll())
                {
                    DirectoryEntry de = resEnt.GetDirectoryEntry();
                    string name = de.Properties[ADUserProperties.sAMAccountName].Value.ToString().ToLower();
                    if (name == sAMAccountName.ToLower())
                    {
                        temp = resEnt.GetDirectoryEntry();
                        break;
                    }
                }
            }
            catch
            { }
            return temp;
        }