Looking through a group in Active Directory and listening all Groups with all users until level 3

I have a problem with my C# code where I want to display all groups under one specific group, called L_P001xxx.

What I want in the end is that beginning with the group L_P001xxx and I want to display all groups until level 3 and in level 3 I want to display only the users.

I think I have to solve this with a recursion, but it is not working as intended.

Now what I get is this:

First member, called A96XYZ of this group, then the first user of this group, but after that it is stuck and I do not know why.

This is my error message:

{"Unknown name. (Exception from HRESULT: 0x80020006 (DISP_E_UNKNOWNNAME))"}

This is my code:

namespace ADQuery
{
    class Program
    {
        static void Main(string[] args)
        {
        DirectoryEntry root = new DirectoryEntry(String.Format("WinNT://{0},Computer", "10.18.6.9"), null, null, AuthenticationTypes.Secure);
        DirectoryEntry admGroup = root.Children.Find("L_P00142W", "group");
        DoForEveryNode(admGroup);
    }

    static void DoForEveryNode(DirectoryEntry de)
    {
        object members = de.Invoke("members", null);
        foreach (object groupMember in (IEnumerable)members)
        {
            DirectoryEntry member = new DirectoryEntry(groupMember);
            Console.WriteLine(member.Name);
            DoForEveryNode(member);
        }
    }
}
}

I did a little more work and now it is possible for me to read the users of each group but there is still one little problem.

I have this group L_P00142W, and this group has a Domain Local Groups, called L_ext_P00142W, and this group I cannot access.

All the other groups are not a problem anymore to read for me, but this group is always ignored. Maybe someone knows what I can do or should do? Here is my code:

namespace ADQuery
{
class Program
{
    static void Main(string[] args)
    {
        //GetUserLocalGroups("L_P00142", "10.18.6.9", "s-gruppe");
        DirectoryEntry root = new DirectoryEntry(String.Format("WinNT://{0},Computer", "ip-address"), null, null, AuthenticationTypes.Secure);
        DirectoryEntry admGroup = root.Children.Find("L_P00142W", "group");
        DoForEveryNode(admGroup);
    }

    static void DoForEveryNode(DirectoryEntry de)
    {
        if (de.SchemaClassName == "Group")
        {
            object members = de.Invoke("members", null);
            foreach (object groupMember in (IEnumerable)members)
            {
                DirectoryEntry member = new DirectoryEntry(groupMember);
                if (member.SchemaClassName == "User")
                    Console.WriteLine("I am a user: " + member.Name);
                else
                {
                    Console.WriteLine("I am a group: " + member.Name);
                    DoForEveryNode(member);
                }
            }
            Console.ReadLine();
        }
    }
}
}