public static void AddUserToGroup(string userDistinguishedname, string groupDistinguishedName)
        {
            DirectoryEntry group = new DirectoryEntry("LDAP://ldap.mydomain.com/" + groupDistinguishedName);
            DirectoryEntry user = new DirectoryEntry("LDAP://ldap.mydomain.com/" + userDistinguishedname);
            group.Username = "Administrator";
            group.Password = "myAdminPassword";

            using (group) //group is your DirectoryEntry for group
            {
                //member if your user DirectoryEntry
                group.Invoke("Add", new string[] { user.Path });
            }
        }


        public static void RemoveUserFromGroup(string userDistinguishedname, string groupDistinguishedName)
        {
            DirectoryEntry group = new DirectoryEntry("LDAP://ldap.mydomain.com/" + groupDistinguishedName);
            DirectoryEntry user = new DirectoryEntry("LDAP://ldap.mydomain.com/" + userDistinguishedname);
            group.Username = "Administrator";
            group.Password = "myAdminPassword";


            using (group) //group is your DirectoryEntry for group
            {
                //member if your user DirectoryEntry
                group.Invoke("Remove", new string[] { user.Path });
            }
        }