C#: code error while changing the active directory user's password

C# code     

> error--->>>Unknown name. (Exception from HRESULT: 0x80020006
> (DISP_E_UNKNOWNNAME))

and the code is this

using (DirectoryEntry entry = new DirectoryEntry("LDAP://admin-jyt69gl7t.hello/CN=Users,DC=hello"))
{
    entry.Username = username;
    entry.Password = strOldPassword;

    DirectorySearcher searcher = new DirectorySearcher(entry);

    try
    {
        searcher.FindOne();
        entry.AuthenticationType = AuthenticationTypes.Secure;
        entry.Invoke("ChangePassword", new object[] { strOldPassword, strNewPassword });
        //  oDE.Invoke("SetPassword", new object[] { strNewPassword });
        entry.CommitChanges();
    }
    catch (Exception excep)

I am getting this exception

> Unknown name. (Exception from HRESULT: 0x80020006
> (DISP_E_UNKNOWNNAME))

Simply follow the code under

using System.DirectoryServices;


private DirectoryEntry GetUser(string UserName)

{

    DirectoryEntry de = GetDirectoryObject();
    DirectorySearcher deSearch = new DirectorySearcher();
    deSearch.SearchRoot = de;

    deSearch.Filter = "(&(objectClass=user)(SAMAccountName=" + UserName + "))";
    deSearch.SearchScope = SearchScope.Subtree;
    SearchResult results = deSearch.FindOne();

    if (!(results == null))
    {
       // **THIS IS THE MOST IMPORTANT LINE**
       de = new DirectoryEntry(results.Path, "username", "password", AuthenticationTypes.Secure); 
       return de;
    }
    else
    {
       return null;
    }
}

private DirectoryEntry GetDirectoryObject()

{

    DirectoryEntry oDE;
    oDE = new DirectoryEntry("LDAP://192.168.1.101", "username", "password", AuthenticationTypes.Secure);
    return oDE;
}


 public static bool ChangePassword(string UserName, string strOldPassword, string strNewPassword)

        {

            bool passwordChanged = false;

            DirectoryEntry oDE = GetUser(UserName, strOldPassword);

            if (oDE != null)
            {
                try
                {
                    // Change the password.
                    oDE.Invoke("ChangePassword", new object[] { strOldPassword, strNewPassword });
                    passwordChanged = true;
                }
                catch (Exception ex)
                {
                    Debug.WriteLine("Error changing password. Reason: " + ex.Message);

                }
            }
            return passwordChanged;
        }